With continued American aid to Ukraine stalled and against the looming prospect of a second Trump presidency, NATO officials are looking to take more control of directing military support from Ukraine’s allies — a role that the United States has played for the past two years.

Under a proposal being discussed this week at the military alliance’s headquarters, NATO would oversee the Ukraine Defense Contact Group, a group currently led by the United States that coordinates the donation and delivery of weapons to the battlefield. Discussions are also underway about a plan floated by Jens Stoltenberg, the NATO secretary general, to secure an additional $100 billion from the alliance’s 32 member states for Ukraine over five years.

“A stronger NATO role in coordinating and providing support is the way to end this war in a way where Ukraine prevails,” Mr. Stoltenberg said on Wednesday at the start of meetings among the alliance’s top diplomats.

“There is a need to give this a more robust and institutional framework to ensure predictability and commitment for the long haul,” Mr. Stoltenberg said. He added: “I strongly believe it’s important that allies make decisions fast. And that includes, of course, the United States.”

Mr. Stoltenberg would not discuss specifics, but he said he hoped to have the new efforts approved in time for a July summit meeting of NATO leaders in Washington, where officials are expected to again debate when Ukraine might be allowed to join the military alliance, as has been promised for years.

A NATO official confirmed the proposals, which were reported earlier by news outlets including Bloomberg News.

It is not clear whether they will be approved at all, however. A second NATO official said that Hungary, where Prime Minister Viktor Orban has maintained warm relations with Russia, opposed the effort to put the Defense Contact Group under the alliance’s oversight. And several allies have questioned how NATO would be able to corral the $100 billion when it has no leverage to raise money among member states, the official said. Both NATO officials spoke on the condition of anonymity, because the details of the plans have not been publicly released.

It was also unclear whether Washington would support such changes. Lloyd J. Austin III, the American defense secretary, called the group’s current format “a very effective forum” when asked last month about the prospect of moving it into NATO. Secretary of State Antony J. Blinken was delayed in arriving to Wednesday’s meeting but was expected to attend.

The alliance has previously been reluctant to take on a greater role in the war in Ukraine, given fears of provoking a wider and more severe military response from President Vladimir V. Putin of Russia, who already views the conflict as a proxy war between his nation and NATO.

But Washington’s support for Ukraine has wavered in recent months. The United States has continued to wrangle over a $60 billion aid package for Ukraine that congressional Republicans have stalled for six months, although Speaker Mike Johnson is expected to try to push through legislation when lawmakers return to Washington next week.

The delay has infuriated Ukraine, irritated allies and prompted Mr. Stoltenberg to declare on Wednesday that it “has consequences” on the battlefield, where Ukraine’s forces are running out of artillery and air defense systems as Russia gains ground in key areas along the front line.

Concern is also growing among NATO allies over the possible re-election in November of former President Donald J. Trump, who in the past has vowed to withdraw the United States from the military alliance and recently threatened not to defend Europe if it were under attack. Mr. Stoltenberg sidestepped a question on Wednesday about Mr. Trump, but said that “you need long-term planning” for NATO to continue supporting Ukraine.

In the two years since Russia’s full-scale invasion of Ukraine, the United States has led an effort to funnel more than $88 billion in weapons and security assistance to Kyiv through the Ukraine Defense Contact Group, which usually meets at an American air base in Ramstein, Germany. The group includes about 50 countries and international organizations, including some that are not NATO members.

It is not clear how the NATO alliance would work with nonmember states. But Mr. Stoltenberg noted that NATO states provide 99 percent of the military aid that Ukraine receives. He also said what was “obvious is that we need new and more money for Ukraine, and we need it over many years.”

Beyond the new proposals, NATO has little to offer Ukraine for the rest of the year, especially given that the United States and Germany insist that Kyiv must make democratic and security reforms before it can become an alliance member.

Ukraine’s foreign minister, Dmytro Kuleba, is scheduled to meet top NATO diplomats at headquarters on Thursday, the official 75th anniversary of the military alliance that was created at the start of the Cold War in a collective security pact against the Soviet Union.

Its latest member is Sweden, which abandoned decades of nonalignment after Russia invaded Ukraine in 2022. Sweden joined the alliance formally this year, and Wednesday was the first time its foreign minister, Tobias Billström, joined the diplomatic discussions as a full NATO member.

Matina Stevis-Gridneff contributed reporting.

Donald J. Trump, appearing in two crucial swing states on Tuesday, avoided discussing abortion but teased that he would address the issue “next week,” once again demurring on taking a clear position on the issue after two Florida Supreme Court rulings shook up the 2024 campaign in the former president’s home state.

The conservative top court in Florida on Monday allowed a strict six-week abortion ban to take effect in May while also allowing a proposed constitutional amendment to be placed on the ballot that would guarantee access to abortion “before viability,” or at about 24 weeks.

The rulings present a potential new vulnerability for Mr. Trump in the presidential race. Florida has become steadily more conservative in recent years, placing most statewide elections well out of reach for the Democratic Party. But the two decisions will elevate abortion — an issue that has carried many races for Democrats in recent years — to a position of prominence both on the campaign trail and on the ballot.

The former president indicated last month that he was likely to back a 15-week federal ban on abortion, while adding that he thought abortion should be a state issue — and that anti-abortion activists who wanted a ban earlier in pregnancy should understand that “you have to win elections.”

Mr. Trump did not otherwise address abortion in his campaign appearances on Tuesday in Grand Rapids, Mich., and Green Bay, Wis. Mr. Trump said that “we’ll make a statement next week on abortion” after being asked by a reporter in Grand Rapids if he supported the six-week ban in Florida. The pro-Trump crowd tried to drown out the question with boos and began chanting “four more years” and “U.S.A.” as Mr. Trump walked away.

Representatives of the Trump campaign did not immediately respond to questions about the abortion announcement and where that would fit into Mr. Trump’s campaign schedule. The former president has often promised policy plans — for example on infrastructure or health care — that are either delayed or never delivered.

President Biden and his campaign pounced on Mr. Trump’s promise of a coming abortion announcement. “You already made your statement, Donald,” Mr. Biden wrote on social media, along with a statement from Mr. Trump last year bragging that he “was able to kill Roe v. Wade” and that “without me there would be no six weeks, 10 weeks, 15 weeks, or whatever is finally agreed to.”

Sarafina Chitika, a spokeswoman for the Biden campaign, said in a statement that “Trump is ‘proud’ he overturned Roe v. Wade, and he is responsible for every extreme abortion ban, every attack on contraception and every cruel, dangerous restriction placed on women because of it.”

Mr. Trump has spoken often of the electoral advantage for Democrats on the issue. He has repeatedly complained that Republicans don’t know how to talk about abortion and has said that if conservative politicians “don’t speak about it correctly, they’re not going to win.” He has also previously singled out the six-week ban in Florida, signed by Gov. Ron DeSantis, his former rival for the nomination, as “a terrible thing and a terrible mistake.”

Mr. Trump’s campaign had put out a statement addressing the court decisions in Florida before Mr. Trump took the stage on Tuesday. Brian Hughes, a senior adviser for the campaign, said Mr. Trump “supports preserving life but has also made clear that he supports states’ rights because he supports the voters’ right to make decisions for themselves.”

Michael Gold contributed reporting from Green Bay, Wis., and Anjali Huynh from Grand Rapids, Mich.

Former President Donald J. Trump again cast President Biden’s immigration record in violent and ominous terms on Tuesday, accusing him in two speeches in battleground states of creating a “border blood bath” and once more using dehumanizing language to describe some migrants entering the country illegally.

In a speech in Grand Rapids, Mich., Mr. Trump, flanked by law enforcement officers, reiterated his baseless claim that other countries were sending “prisoners, murderers, drug dealers, mental patients and terrorists, the worst they have” to the United States. Immigration officials have said that most of the people crossing the border are members of vulnerable families escaping poverty and violence.

Mr. Trump also used his speech, which lasted roughly 45 minutes, to defend his use of dehumanizing language to refer to immigrants accused of crimes. After referring to the man who the authorities say killed a 22-year-old nursing student in Georgia in February, Mr. Trump said: “Democrats said please don’t call them ‘animals.’ I said, no, they’re not humans, they’re animals.”

Mr. Trump drew attention last month when, while discussing the U.S. auto industry, he predicted a “blood bath for the country” should he lose in November. After critics accused him of stoking violence, Mr. Trump and his allies pointed back to Mr. Biden, insisting he was responsible for a “blood bath” because of his immigration policies.

The former president has repeatedly criticized Mr. Biden, accusing him of maintaining lax border security that he blames for violent crime, though available data does not support the idea that migrants are contributing to increases in crime.

Mr. Trump’s campaign appears to be trying to turn “blood bath” into a catchphrase, essentially trolling his critics and shifting the focus to Mr. Biden. On Tuesday, the Republican National Committee, which the Trump campaign now effectively controls, introduced a website, BidenBloodbath.com, that mirrors Mr. Trump’s argument that Mr. Biden is responsible for an “invasion” at the United States’ border with Mexico. The site highlights a number of violent crimes in which undocumented immigrants have been accused.

But his remarks in Michigan and at a rally later in Green Bay, Wis., also demonstrated how the former president has tried to stoke fears around immigration and border security in the 2024 election, a tactic he used effectively in 2016. Republicans have been eager to keep the issue at the top of voters’ minds in a bid to chip away at Mr. Biden’s support.

“This is country-changing, it’s country-threatening, and it’s country-wrecking,” Mr. Trump said in Michigan of migrants crossing the southern border. “They have wrecked our country.”

Democrats have pushed back against that framing. Ahead of Mr. Trump’s visit, the Democratic National Committee put up billboards near Grand Rapids referring to a bipartisan border bill that fell apart in the Senate after Mr. Trump pressed Republicans to block it. The billboards claimed that “Donald Trump broke the border” and that the former president wanted only “chaos, not solutions.”

Mr. Trump’s speeches in both states were his first campaign events after a weekslong break from the trail, during which he raised money, contended with legal issues and blasted his political and legal opponents on social media.

Mr. Trump has seized on high-profile crimes involving immigrants to try to make inroads in key battleground states, including Michigan and Wisconsin, connecting the influx of migrants at the southern border to states hundreds of miles away.

On Tuesday, he said that “once peaceful suburban Michigan” was coming “under an invasion” and spoke of the recent killing of Ruby Garcia, who was found dead on the side of a highway in Grand Rapids last month. The authorities have said that Ms. Garcia was dating the man accused of killing her, who entered the country illegally as a child and was deported to Mexico in 2020.

Michigan Democrats blasted Mr. Trump’s references to Ms. Garcia in remarks before his appearance. Senator Debbie Stabenow, Democrat of Michigan, said Mr. Trump was “exploiting” Ms. Garcia’s death and called his response “shameful.” And while Mr. Trump said in Michigan that he had spoken with some of Ms. Garcia’s family, her sister told a local television station that Mr. Trump “did not speak with us.”

Ahead of Mr. Trump’s speech in Michigan, his campaign handed out packets to reporters that highlighted other people who the campaign said had been affected by crimes involving undocumented immigrants. They included Laken Riley, the Georgia nursing student whose death has become a flashpoint among Republicans. The authorities say Ms. Riley was killed by a Venezuelan migrant who had entered the country illegally.

Pete Hoekstra, the chair of the Michigan Republican Party, said that “it’s clear immigration and the economy are going to dominate the debate here in Michigan.” He added that he believed voters in the state “look at what’s happening on the border, and it’s hard for them to believe exactly what they’re seeing, that there’s no rule of law.”

Both Michigan and Wisconsin were part of the so-called blue wall that Democrats had counted on for two decades before the 2016 race, when Mr. Trump won over working-class white voters who are key parts of the electorate in both states.

Mr. Biden won both states in 2020, although Mr. Trump falsely claimed during his rally in Wisconsin, which held its presidential primaries on Tuesday, that he had won there “by a lot” and insisted that the election had been stolen from him.

Democrats also won governors’ races in both states in 2018 and defended their seats in 2022, in part by making protecting abortion access central to their races.

The party continued its efforts on Tuesday to make abortion rights a key campaign issue. Though Mr. Biden did not hold public campaign events, his campaign seized on a ruling by the Florida Supreme Court on Monday that allowed the state’s six-week abortion ban but also put abortion access on the ballot there this fall.

There is little indication that Mr. Biden will devote significant time and resources to competing in Florida. But his campaign released a television ad that it plans to run in battleground states — including Michigan and Wisconsin — that attacked Mr. Trump for statements claiming credit for the Supreme Court’s decision to overturn Roe v. Wade in 2022.

A senior adviser to the Trump campaign, Brian Hughes, addressed the ruling in Florida, saying in a statement that Mr. Trump supports states’ rights and thinks “voters should have the last word.”

Mr. Trump did not mention abortion, or his role in appointing three of the Supreme Court justices who helped overturn Roe, at either event. But after his remarks in Michigan, he responded to a reporter’s question about the Florida ruling by saying that his campaign would “be making a statement next week” on abortion.

A spokeswoman for the Democratic National Committee, Aida Ross, said in a statement: “We don’t need to wait until next week to know where Donald Trump stands on abortion — he has been peddling the same anti-choice extremism for years.”

Reid J. Epstein contributed reporting from Washington.

In the hours before delivering his State of the Union speech last month, President Biden called the chief executives of General Motors and Cisco Systems to ask their advice on the state of the American economy and share how he planned to talk about it.

Then he rode to Capitol Hill and, in his address, promised to raise the rate on a new minimum tax his administration has levied on big companies “so every big corporation finally begins to pay their fair share.”

“I also want to end tax breaks for Big Pharma, Big Oil, private jets, massive executive pay,” Mr. Biden continued, adding: “End it now.”

The sequence epitomizes Mr. Biden’s alternatively cozy and combative relationship with America’s business leaders, which has rippled through the national economy, federal policy and now the 2024 campaign for the White House.

The president has both courted and pilloried corporate America as he seeks re-election this fall. Corporate leaders have enjoyed record profits on his watch and an open channel with his administration, but they have bristled at some of his biggest policy decisions.

There is a certain symbiosis with corporate leaders in much of Mr. Biden’s economic agenda. His industrial policy initiatives depend heavily on corporate tax incentives, which he champions at ribbon-cuttings nationwide: The climate and advanced-manufacturing laws that Mr. Biden signed in 2022 feature large tax cuts for corporations that invest in the production of semiconductors, solar panels and other strategic goods. Republicans have derisively called those incentives “corporate welfare.”

Mr. Biden frequently seeks executives’ counsel on a wide variety of economic issues, including supply chain snarls, infrastructure investments and worker training. He impressed Calvin Butler, the chief executive of the utility giant Exelon, in a two-hour meeting in the Oval Office with executives last fall.

“He was engaged in it, and I can tell you this,” Mr. Butler said in an interview. “At about the hour mark, they kept tapping on him to say, ‘Hey, you know, we got other things to do.’ But he wanted to keep it going. He wanted to keep talking.”

As he seeks re-election, though, Mr. Biden has leaned heavily into populist attacks on the executives and companies he has engaged. He loves to talk about raising corporate taxes. He has also taken to blaming big companies, sometimes by name, for raising prices on some consumer staples. He blasts others for shrinking portions of snack foods, like candy bars, without cutting their prices.

Mr. Biden has also brought to office an economic philosophy that relies heavily on federal government intervention in private markets. That includes investments in infrastructure and industries, which business leaders generally support.

But it also includes environmental, financial and other regulations meant to reduce risks in the marketplace. Businesses oppose those efforts, along with the administration’s aggressive antitrust enforcement and other initiatives meant to stimulate competition.

As a result, Mr. Biden’s relationship with corporate America “is a complicated one,” said Neil Bradley, the executive vice president and chief policy officer at the U.S. Chamber of Commerce, a large business lobbying group in Washington.

Mr. Biden and his economic team have been open and thorough in their outreach to business groups, Mr. Bradley said, but frustrating in their policy choices. Chamber officials calculate that federal agencies under Mr. Biden have issued about twice as many regulations considered “economically significant” — currently defined as carrying at least a $200 million annual effect on the economy — as they did under President Donald J. Trump.

It is a contrast with Mr. Trump, whose administration employed less consistent outreach and careened chaotically from crisis to crisis. Mr. Bradley said executives were torn on which combination they preferred.

“You can look at a Trump administration with a lot more uncertainty, but directionally, the regulatory effort was moving to lighten the regulatory costs,” he said. “Here in the Biden administration, we have a pretty good idea where they’re going to go — it’s just how crushing is it going to be in terms of the regulatory level? And so, interestingly, there’s a lot of people saying, ‘The chaos is better.’”

Mr. Biden speaks regularly with leaders from large corporations and small businesses, and he has visited dozens of companies while in office. Executives who have spoken with the president and his aides say they listen earnestly to companies’ concerns, even when Mr. Biden and his team make clear that they disagree on the policy matter at hand.

Mr. Butler of Exelon said he had urged Mr. Biden at the White House to move faster to clear permitting issues and other hurdles to the building out of new-energy infrastructure. Mark Cuban, the famed investor and a founder of Cost Plus Drugs, said in an email that his conversations with Mr. Biden largely focused on health care, including what he called the “great job” that the president had done in getting Medicare to negotiate lower prescription drug prices.

Brad Smith, the chief executive of Microsoft, said in an interview that he had talked with Mr. Biden about carrying out his infrastructure bill and the CHIPS and Science Act, along with regulation of artificial intelligence. He praised Mr. Biden’s efforts to strengthen cybersecurity, saying he has “done more in his presidency than any president ever” on that issue.

Mr. Biden’s staff, Mr. Smith added, “has a breadth of expertise that is being applied at a deep level.” Under Mr. Trump, “the staff was leaner,” he said. “There weren’t as many in a lot of key jobs.”

Other executives have criticized Mr. Biden’s policies, all or in part. Oil and gas executives have denounced an administration pause on the permitting of new natural gas export terminals. Jamie Dimon, the chief executive of JPMorgan Chase, called Mr. Biden’s climate law and other green energy initiatives “inflationary” in an interview with CNBC this year.

Ken Griffin, the founder of the financial firm Citadel and a major Republican donor, swiped at Mr. Biden’s economic pitch in a Bloomberg interview in November. “Whoever told him to run on Bidenomics has no idea how to read an economics textbook,” Mr. Griffin said.

The Biden outreach to executives is similar to the approach employed by President Barack Obama and his team, according to business leaders and administration officials who also served under Mr. Obama.

But Mr. Biden differs from Mr. Obama — and Mr. Trump — in several respects. Executives who have spoken with him say the president makes clear in conversations that he is a “labor guy,” who measures economic success in part by the creation of well-paying union jobs. He has embraced robust federal scrutiny of mergers and other antitrust issues to a degree that even Mr. Obama did not.

He also has deeper policy entanglements with corporate behavior. Mr. Biden’s climate agenda blends corporate tax sweeteners for domestic production with a strict wave of regulations meant to quickly reduce fossil-fuel emissions. In some cases, agencies under Mr. Biden have softened some regulatory proposals in their final form — explicitly, administration officials say, to address corporate concerns.

Lael Brainard, who leads the White House National Economic Council, said in an interview that the president’s targeted corporate tax breaks were a departure from a Republican philosophy that pushed “across-the-board tax breaks for businesses, regardless of whether they were making investments that are good for America, generate jobs, help with a clean energy transition.”

Democratic pollsters are encouraging Mr. Biden to amplify that message in his re-election campaign. They want him to emphasize his plans to raise taxes for big companies while calling out firms for raising prices to pad profits and saddling customers with “junk fees” for things like concert tickets. Their data suggest that corporate taxation is a key vulnerability this fall for Mr. Trump, who cut corporate tax rates while in office and is set to face Mr. Biden in a 2020 rematch.

Voters “want to feel the president is on their side against people they think are squeezing them,” said Evan Roth Smith, the lead pollster at the Democratic group Blueprint. “Voters have no sympathy for big companies right now,” he added.

Mr. Bradley of the U.S. Chamber of Commerce said many executives bristled at that language, and in particular at Mr. Biden’s practice of calling out companies by name for raising prices or shrinking portions. But some executives dismiss or downplay Mr. Biden’s tax proposals — and repeated calls for companies to pay their “fair share” — as campaign bluster.

“Recognizing how D.C. works, and that we’re in a political season, I tend not to get too high or too low on any of that,” Mr. Butler said.

Mr. Smith of Microsoft said it was an area of disagreement in an otherwise positive relationship with the president.

“We’re not going to be the first company to sign up for tax increases,” he said. But, he added later, “I think our tax rate is high enough that our initial reaction is, typically, that he’s talking about someone else.”

Former President Donald J. Trump has refused to accept his loss in the 2020 election, painted as martyrs the supporters who stormed the Capitol on Jan. 6, 2021, laid groundwork to deny the 2024 election results if he loses, and said he would be a dictator on his first day back in office if he wins.

But according to the independent presidential candidate Robert F. Kennedy Jr., it is President Biden who poses the greater threat to American democracy — a view that Mr. Kennedy shares with Mr. Trump himself, and that democracy experts called “absurd” and “preposterous.”

Such a perspective is possible because Mr. Kennedy, who has founded his political career on promoting vaccine misinformation and conspiracy theories about the government, sees the Biden administration’s efforts to curtail the spread of misinformation as a seminal issue of our time. Censorship, as he calls it, overpowers all other concerns about the political system.

Mr. Kennedy’s stance drew fresh scrutiny this week after he said in an interview on CNN, “President Biden is a much worse threat to democracy, and the reason for that is President Biden is the first candidate in history, the first president in history that has used the federal agencies to censor political speech, to censor his opponent.” He repeated himself on Fox News on Tuesday, saying that a president like Mr. Biden was “a genuine threat to our democracy.”

The remarks by Mr. Kennedy, who carries the name but not the support of a storied Democratic family, were an escalation of his attacks on Mr. Biden and the Democratic Party — and he quickly backtracked, saying in an interview with Chris Cuomo on NewsNation on Tuesday night that he had been misunderstood. “What I said was that I could make this argument. I didn’t say definitively whether I believed one or the other was more dangerous to democracy. I did say that I don’t believe either of them are going to destroy democracy.”

Mr. Kennedy has long said that the government’s engagement with media companies and tech platforms — to prevent the spread of disinformation or illegal materials or, in Mr. Kennedy’s case, the arguments he and his allies made against vaccines — amounts to illegal censorship, an argument that was met with skepticism at the Supreme Court last month.

In the CNN and Fox News interviews, Mr. Kennedy — an environmental lawyer who until last fall was himself a Democrat — trained his outrage directly on the Democratic Party’s leader, whose allies worry that Mr. Kennedy could tip a close election in November to Mr. Trump.

Democratic officials have devoted increasing resources to a multipronged effort to undermine Mr. Kennedy’s campaign, fearing that his presence on swing-state ballots could siphon votes from Mr. Biden.

At the same time, it remains unclear whether Mr. Kennedy — whose anti-establishment message has also made him popular with some disaffected Republicans, independents and Libertarians — would draw more votes from Mr. Biden than from Mr. Trump. A recent Fox News poll showed him drawing about equally from both candidates, and Mr. Trump attacked Mr. Kennedy last week as a “radical Left” candidate, in a potential sign of nervousness about his candidacy.

In campaign appearances, Mr. Kennedy has often drawn comparisons between Mr. Biden and Mr. Trump. Last week, when he announced his running mate, Nicole Shanahan, a Silicon Valley lawyer, Mr. Kennedy said that to young Americans, Mr. Biden and Mr. Trump “look like two sides of the same coin.”

But several scholars who have studied democratic governments and the ways they can backslide told The New York Times that it was nonsensical to suggest that social media moderation — which the Supreme Court seemed inclined to uphold as a legitimate goal of government — posed a greater threat than what Mr. Trump has done.

They pointed to his refusal to accept an election loss, his stoking of political violence, and his efforts to consolidate executive power and undermine public confidence in independent sources of information.

The two most fundamental tenets of democracy are that politicians “must always unambiguously accept the results of elections and must always unambiguously reject political violence,” said Steven Levitsky, a professor of government at Harvard who co-wrote the book “How Democracies Die.” “I don’t think you’ll find a democracy expert in the world who will claim that the mild efforts to regulate social media in the United States are somehow equivalent or worse than an effort to overturn an election or the encouragement of political violence.”

Sheri Berman, a professor of political science at Barnard College, said Mr. Kennedy had not only downplayed Mr. Trump’s election denial — a threat that is “fundamental” and “has to be recognized as such if democracy is going to work,” she said — but also inflated Mr. Biden’s actions.

“If we had a president who was using federal agencies to chase down his opponents, to disadvantage them politically, to stop them from being able to speak to citizens and voters, that would be a major infringement of democratic norms,” Dr. Berman said. “That’s not what Biden was doing.”

In the CNN interview, Mr. Kennedy said Mr. Trump’s attempt to overturn the 2020 election “clearly” was a threat, but added: “The greatest threat to democracy is not somebody who questions election returns, but a president of the United States who uses the power of his office to force a social media company — Facebook, Instagram, Twitter — to open a portal and give access to that portal to the F.B.I., the C.I.A., the I.R.S., the CISA, the N.I.H., to censor his political critics.”

He then said he was not making the argument he had just made, but was simply saying it was an argument he could make.

He also did not provide evidence of any “portal” through which federal agencies can remove posts. Rather, he referred to a lawsuit he filed last year alleging that, by threatening regulatory action, the Biden administration had “induced” social media companies to restrict speech — including anti-vaccine misinformation — in ways the First Amendment would prohibit the government from doing directly.

A federal judge in February granted a preliminary injunction but stayed it until the Supreme Court rules in a related case, Murthy v. Missouri, with which Mr. Kennedy’s case was consolidated. In the meantime, the Supreme Court allowed the government, including the F.B.I., to continue contact with major social media companies — and in hearing the case last month, the justices appeared skeptical of the arguments against the government.

A lawyer for the government, Brian H. Fletcher, told the court that banning the regulation in question would itself prohibit speech, including public comments from a press secretary or other officials seeking to discourage posts that are harmful to children, antisemitic or Islamophobic. He added that the social media companies had acted independently of the government and often rejected requests to take down postings.

A senior adviser for the Democratic National Committee called Mr. Kennedy’s comments “MAGA talking points” that put to rest “any doubts that he’s a spoiler candidate.”

“With a straight face, Robert F. Kennedy Jr. said that Joe Biden is a bigger threat to democracy than Donald Trump because he was barred from pushing conspiracy theories online,” the adviser, Mary Beth Cahill, said. “There is no comparison to summoning a mob to the Capitol and promising to be a dictator on Day 1.”

In the CNN interview, Mr. Kennedy also said falsely that Mr. Biden was “the first president in history to use his power over the Secret Service to deny Secret Service protection to one of his political opponents for political reasons,” referring to the government’s refusal so far to extend protection to Mr. Kennedy.

“Major” presidential candidates are eligible for Secret Service protection but are not guaranteed it. Whether to grant protection is up to the secretary of homeland security, in consultation with congressional leaders from both major parties, and independent and third-party candidates are less likely than Democrats and Republicans to receive it.

In a fund-raising email on Tuesday morning, Mr. Kennedy’s campaign reiterated its complaints about the Biden administration and the Democratic Party, describing the party as corrupt and attacking its escalating legal efforts to challenge his ballot access and its refusal to allow a debate between Mr. Kennedy and Mr. Biden.

“The Democrat political machine is pulling out every trick in the book to stop our huge momentum,” the email said. “With endless resources, establishment Democrats want to stop a debate between Robert F. Kennedy Jr. and Biden. They are using a vast network of shadowy dark money groups and vicious attorneys to keep Kennedy-Shanahan ticket off state ballots and spread malicious smears.”

Dr. Levitsky and Dr. Berman both noted that it was rare, in a democratic country, for a politician to explicitly reject democratic norms. It is more common for them to try to create a cloud of doubt so voters struggle to know what is true.

“Those who engage in misinformation about democracy, those who muddy the waters about what is and isn’t democratic, are complicit in the assault on our democracy,” Dr. Levitsky said. “The kind of behavior that sustains a democracy hasn’t changed over time.”

The U.S. warning to Russia ahead of a terrorist attack near Moscow was highly specific: Crocus City Hall was a potential target of the Islamic State, according to U.S. officials.

The warning had the right venue but imprecise timing, suggesting that the attack could come within days. Indeed, the public warning by the United States Embassy on March 7 warned of potential terrorist attacks in the next two days.

Gunmen stormed the hall on March 22, killing 144 people, the deadliest attack in Russia in nearly 20 years. The Islamic State claimed responsibility for the attack, and Russia charged four men from Tajikistan, accusing them of carrying out the massacre.

But President Vladimir V. Putin and other top officials have continued to claim, without evidence, that Ukraine could have played a role in the attack, a statement that American officials have repeatedly said was baseless.

The news that the U.S. warning specified the precise target of the attack was reported earlier Tuesday by The Washington Post.

The United States works intensely to collect intelligence on potential plots by the Islamic State and its Afghanistan-based branch, ISIS-Khorasan.

Armed with that information, the United States has been able to warn both Russia and Iran, erstwhile adversaries, about specific targets the Islamic State was planning to hit. But in both cases the warnings were not heeded, at least not enough to stop the violence.

Some Western officials said Russia paid some attention to the warning delivered by the C.I.A. station in Moscow, and took steps to investigate the threat. But the new information raises questions about why Russian intelligence failed to maintain higher security levels. At the time of the attack, no additional security measures were in place at the venue.

The Western officials have said that when the attack failed to materialize immediately, Russia appeared to have lowered its guard, potentially considering the American warning false.

On Tuesday, the Russian state-run Interfax news agency reported that Sergei Naryshkin, the head of Russia’s Foreign Intelligence Service, said the American warning was “too general” and, as a result, did not allow authorities to identify the potential attackers.

The White House, C.I.A. and other intelligence officials declined to comment on the new details of the warning. But White House officials have previously acknowledged the broad warning given to Russia.

Days before the attack, Mr. Putin was disparaging the American warnings, saying they were “outright blackmail” and attempts to “intimidate and destabilize our society.”

While Russian security services were focused on terrorism decades ago, they are now focused on Mr. Putin’s domestic opponents.

Experts have said the crackdown has diluted the focus on terrorism by the security services, potentially contributing to the failure to be able to use the American warning to prevent the attack.

While at first glance it might seem odd that the United States would tell an adversarial country like Russia of an attack, under law American intelligence agencies have a “duty to warn.” If spy agencies learn about a potential attack, they must tell the target, to enable them to take steps to protect themselves.

But the war in Ukraine, and U.S. military support for Kyiv, has created tension and suspicion between Moscow and Washington not seen since the Cold War. That appears to have led Mr. Putin and his top aides to dismiss the American warning.

In an open display of frustration, federal prosecutors on Tuesday night told the judge overseeing former President Donald J. Trump’s classified documents case that a “fundamentally flawed” order she had issued was causing delays and asked her to quickly resolve a critical dispute about one of Mr. Trump’s defenses — leaving them time to appeal if needed.

The unusual and risky move by the prosecutors, contained in a 24-page filing, signaled their mounting impatience with the judge, Aileen M. Cannon, who has allowed the case to become bogged down in a logjam of unresolved issues and curious procedural requests. It was the most directly prosecutors have confronted Judge Cannon’s legal reasoning and unhurried pace, which have called into question whether a trial will take place before the election in November even though both sides say they could be ready for one by summer.

In their filing, prosecutors in the office of the special counsel, Jack Smith, all but begged Judge Cannon to move the case along and make a binding decision about one of Mr. Trump’s most brazen claims: that he cannot be prosecuted for having taken home a trove of national security documents after leaving office because he transformed them into his own personal property under a law known as the Presidential Records Act.

The prosecutors derided that assertion as one “not based on any facts,” adding that it was a “justification that was concocted more than a year after” Mr. Trump left the White House.

“It would be pure fiction,” the prosecutors wrote, “to suggest that highly classified documents created by members of the intelligence community and military and presented to the president of the United States during his term in office were ‘purely private.’”

At a hearing last month in Federal District Court in Fort Pierce, Fla., Judge Cannon herself expressed skepticism about Mr. Trump’s assertion, saying it was most likely not enough to dismiss the case before it went to trial.

But then within days, she made a surprising move, ordering the former president’s lawyers and Mr. Smith’s prosecutors to send her proposed jury instructions suggesting she was open to embracing the very same defense.

Her order sought language from both sides meant to help jurors understand how the Presidential Records Act might affect the accusation that Mr. Trump had taken “unauthorized possession” of the documents he removed from the White House. For Mr. Trump to be found guilty under the Espionage Act, the central statute in his indictment, prosecutors will have to prove that the former president was not authorized to hold on to more than 30 highly sensitive documents after he left office.

Judge Cannon’s order for jury instructions was odd on its face because such issues are usually hashed out on the eve of trial, and she has not set a trial date yet.

It was even stranger because by appearing to adopt Mr. Trump’s position on the Presidential Records Act, the judge seemed to be nudging any eventual jurors toward acquitting Mr. Trump or even leaving open the possibility that she herself could acquit the former president near the end of the proceeding by declaring that the government had failed to prove its case.

Hoping to forestall either situation, Mr. Smith’s prosecutors told Judge Cannon in their filing on Tuesday that the Presidential Records Act had nothing to do with the case and that the entire notion of submitting jury instructions based on it rested on a “fundamentally flawed legal premise.”

Instead, they asked her to decide the validity of the Presidential Records Act defense in a different way: by rejecting Mr. Trump’s motion to dismiss the case based on the same argument. That motion has been sitting on her desk for almost six weeks.

The prosecutors want Judge Cannon to take that course of action, because any decision she makes on the motion to dismiss can be challenged in an appeals court. But if the case is allowed to reach the jury, any ruling she might make acquitting Mr. Trump cannot be appealed.

Almost from the moment she was assigned the case in June, Judge Cannon, who was appointed by Mr. Trump in his waning days in office, has handled the proceeding in an unorthodox manner.

She has put off making several legal and logistical decisions. And she has spent time at hearings entertaining a series of unusual arguments by Mr. Trump’s lawyers that many federal judges would have rejected out of hand.

The legal gamesmanship she has encouraged over how to handle Mr. Trump’s Presidential Records Act defense is all the more bizarre because the argument itself is legally dubious.

The act was put in place after the Watergate scandal not to permit presidents to unilaterally designate government documents — let alone those containing sensitive state secrets — as their own personal property, but precisely for the opposite reason: to ensure that most records from a president’s time in office remain in the possession of the government.

Moreover, Mr. Trump’s lawyers have never said he officially designated the documents in question as his own. Rather, they have claimed that the designation can be inferred from the fact that he took them from the White House to Mar-a-Lago, his private club and residence in Florida, rather than sending them, as the government says he should have, to the National Archives.

The prosecutors told Judge Cannon in their filing that they interviewed numerous high-ranking White House officials during their investigation — including chiefs of staff, senior members of the White House Counsel’s Office, a national security adviser and top members of the National Security Council — and no one recalled Mr. Trump saying he had designated the records that ultimately wound up in the case as personal.

“To the contrary,” the prosecutors wrote, “every witness who was asked this question had never heard such a thing.”

The dispute about the Presidential Records Act is only one of the many questions that Judge Cannon has failed to resolve in the past few months. The delays could have a profound effect on the case: If it is pushed past the election and Mr. Trump wins, he could order his attorney general to simply dismiss the charges.

Judge Cannon has so far not issued a ruling on a request made in January by Mr. Trump’s lawyers for additional discovery material about the prosecution’s ties to the intelligence community and other national security officials. The lawyers want that information to bolster their claims that members of the so-called deep state conspired to bring the case against Mr. Trump in an effort to sink his political campaign.

The judge is also sitting on a nearly 2-month-old request by Mr. Smith to permit redactions to be made to several of Mr. Trump’s own filings to protect the identities of witnesses who might testify for the government at trial. And she is still considering a host of the former president’s pretrial motions to the dismiss the case.

Should they run out of patience altogether, prosecutors could at some point file a motion asking Judge Cannon to remove herself from the case. She would probably reject that effort, requiring the government to go over her head and make the same request to the U.S. Court of Appeals for the 11th Circuit, which sits above her.

Typically, recusal motions require prosecutors to point to flawed decisions. And so far, Judge Cannon has largely avoided making decisions, complicating any effort to get rid of her.

The Biden administration is pressing Congress to approve a plan to sell $18 billion worth of F-15 fighter jets to Israel, as President Biden resists calls to limit U.S. arms sales to Israel over its military offensive in Gaza.

The State Department recently sent an informal notice to two congressional committees to start a legislative review process for the order, a first step toward the department’s giving formal authorization for the transfer of up to 50 of the planes.

The F-15 order was reported earlier by Politico and CNN and confirmed by two U.S. officials. The deal, which would be one of the largest U.S. arms sales to Israel in years, would also include munitions, training and other support.

Although the United States has expedited some arms for Israel’s current campaign against Hamas, the F-15s would not be delivered for at least five years, the U.S. officials said.

With a top speed of nearly 2,000 miles per hour, the F-15 is capable of both air-to-air combat and bombing targets on the ground. While Israel has used the F-15s it already owns to strike Gaza, its request for the planes appears to reflect longer-term concern about regional threats, including from Lebanon-based Hezbollah, Iran-backed militias in Syria, and Iran itself. The Israel Defense Forces would probably employ F-15s in any potential attack on Iran’s nuclear program.

Israeli officials have also told their U.S. counterparts that Israel is about to place a new order for F-35 jets, a U.S. official said.

The United States steadily delivers weapons to Israel as part of a 10-year agreement to provide $3.8 billion in annual military aid that the Obama administration finalized in 2016. Many arms orders placed since then and that are being filled now have already been approved by Congress.

But the Biden administration has also rushed two new emergency shipments of weapons to Israel totaling more than $250 million since the Oct. 7 terrorist attacks in Israel by Hamas, bypassing congressional approval on the grounds that the arms, mainly artillery and tank ammunition, were needed immediately.

And if Israel’s orders do not meet a certain dollar threshold, then the administration does not need to notify Congress or get its approval. So some orders placed since Oct. 7, perhaps dozens or more, have not been publicly disclosed, U.S. officials said.

Critics of Israel’s campaign in Gaza — in which more than 32,000 Palestinians have been killed, according to health ministry officials there — say that the Biden administration should use any available leverage to make Israel change its approach.

Speaking at a news conference in Paris on Tuesday, Secretary of State Antony J. Blinken did not specifically address the potential F-15 sale. But he defended the Biden administration’s continued transfer of weapons to Israel generally and stressed that most recent ones have not been directly related to the current conflict in Gaza.

Such transfers are part of agreements that “go back a decade or more” and involve weapons systems that can require years to manufacture, Mr. Blinken told reporters. Those cases, he said, “underwent congressional review years ago and were notified years ago, well before the conflict in Gaza started.”

Mr. Blinken indicated that the United States was determined to protect Israel’s wider security concerns, beyond the Gaza conflict.

“It’s also about the threats posed to Israel by Hezbollah, by Iran, by various other actors in the region, each one of which has vowed one way or another to try to destroy Israel,” he said.

After Oct. 7, Israel requested expedited transfers of orders that had been approved years ago, including bombs ranging from 250 pounds to 2,000 pounds, which Israel drops regularly in Gaza but which the U.S. military and many allies prefer not to use in urban warfare.

A State Department official said that the department as a rule does not confirm or deny U.S. arms transfers before they are formally notified to Congress. The official added that after Congress approves an arms sale to Israel, it can be completed in dozens of individual deliveries over many years. These deliveries do not require a separate notification to Congress.

Some U.S. officials privately say that slowing, reducing or conditioning arms sales to Israel might embolden Iran and its regional allies, and weaken Israel’s deterrent power against them.

But critics of Israel’s military campaign in Gaza are unmoved by such arguments, saying that the Biden administration’s repeated calls for Israel to better protect Gazan civilians have had little effect and must be enforced with tangible consequences.

“The Biden administration needs to make better use of the tools we have, including the transfer of offensive weapons, to enforce President Biden’s reasonable requests,” said Senator Chris Van Hollen, Democrat of Maryland.

Mr. Van Hollen, referring to Prime Minister Benjamin Netanyahu of Israel, complained that the “extreme Netanyahu government continues to rebuff the Biden administration at every turn — from disregarding calls to allow more aid to reach starving people in Gaza to insisting that it will launch an invasion of Rafah despite President Biden having drawn a ‘red line.’”

The F-15s were on a list of requests raised last week by Israel’s defense minister, Yoav Gallant, in his meetings with administration officials in Washington, according to a U.S. official briefed on the conversations. Mr. Gallant also said Israel wants to acquire more F-35 fighter jets from the U.S.

That would be separate from Israel’s recently exercising an option in an existing order of F-35s to buy $2 billion more of the jets and equipment.

Israel already owns dozens of F-35s, which are among the most advanced weapons in America’s military arsenal.

It likewise operates a fleet of F-15s, which it has used for strikes in Gaza but also relies on for longer-range missions to places like Lebanon and Syria. In 2016, a senior official in Israel’s air force said that the plane was valuable “when we want to reach far distances with few aircraft.”

An April 1 policy briefing document from the Jewish Institute for National Security for America said that Israel needed F-15 and F-35 fighters to “eliminate Hezbollah personnel and weapons arsenals in Lebanon.”

“Fighter aircraft also provide support to IDF ground forces in Gaza and enable Israel to conduct operations against hostile actors in Syria and elsewhere across the region,” wrote Yoni Tobin, an analyst for the hawkish think tank, which has ties to Israel’s government and military. Mr. Tobin added that the planes were necessary for Israel to maintain decisive military superiority over its regional rivals, known in policy circles as qualitative military edge, or QME.

Speaking to reporters at the White House, John F. Kirby, a White House national security spokesman, said on Tuesday that he believed the administration’s approach was working.

But some in Congress disagree.

“The United States wants Israel to let in more humanitarian aid, stop bombing civilians and not invade Rafah,” Senator Bernie Sanders, independent of Vermont, said on Tuesday. “Netanyahu has ignored all of it. Why are we still sending him taxpayer dollars and weapons and expecting a different outcome?”

Robert Jimison contributed reporting.

President Biden and former President Donald J. Trump won overwhelming victories in state primaries on Tuesday, while a small but significant protest vote in both parties continued to assert itself against each candidate.

Mr. Biden and Mr. Trump, who have already clinched their nominations, scored yawning leads in primaries in Connecticut, New York, Rhode Island and Wisconsin, with the races called shortly after polls closed in each state.

Mr. Trump held at least 75 percent of the vote in every state as of 11 p.m. But Nikki Haley, who dropped out of the race early last month, still took at least 10 percent of the vote in all four states, a sign of lingering discontent in the Republican Party with Mr. Trump’s candidacy. Mr. Trump was weakest in Connecticut, where he notched under 78 percent of the vote, while Ms. Haley took about 14 percent.

Mr. Biden held at least 80 percent of the vote in every primary as of 11 p.m. Activists have urged primary protest votes as a way to register disapproval over Mr. Biden’s handling of the war in Gaza, and the “uncommitted” ballot option took between 8 and 15 percent of the vote in the states where that was an option. In Rhode Island, 14.9 percent of voters chose the “uncommitted” ballot option, or 3,750 votes, with turnout on the Democratic side roughly a quarter of that in 2020.

New York does not have write-in options, so organizers of the “uncommitted” effort urged voters in the Democratic primary to leave their ballots blank instead. Blank ballots will not be reported in the initial, unofficial results of the primary, which showed Mr. Biden with more than 90 percent of tallied votes.

In New York’s Republican primary, Mr. Trump had above 80 percent of the vote, while Ms. Haley had 13 percent and Chris Christie, a former governor of New Jersey, scored more than 4 percent of the vote. He dropped out of the race in January.