For 74 years, the NATO has been America’s most important military alliance. Presidents of both parties have seen NATO as a force multiplier enhancing the influence of the United States by uniting countries on both sides of the Atlantic in a vow to defend one another.

Donald Trump has made it clear that he sees NATO as a drain on U.S. resources by freeloaders. He has held that view for at least a quarter-century.

In his 2000 book, “The America We Deserve,” Trump wrote that “pulling back from Europe would save this country millions of dollars annually.” As president, he repeatedly threatened a U.S. withdrawal from the alliance.

Yet as he runs to regain the White House, Trump has said precious little about his intentions. His campaign website contains a single cryptic sentence: “We have to finish the process we began under my administration of fundamentally reevaluating NATO’s purpose and NATO’s mission.” He and his team refuse to elaborate.

That vague line has generated enormous uncertainty and anxiety among European allies and American supporters of the country’s traditional foreign policy role.

European ambassadors and think tank officials have been making pilgrimages to associates of Trump to inquire about his intentions. At least one ambassador, Finland’s Mikko Hautala, has reached out directly to Trump and sought to convince him of his country’s value to NATO as a new member, according to two people familiar with the conversations.

In interviews over the past several months, more than a half-dozen current and former European diplomats — speaking on condition of anonymity for fear of retribution from Trump should he win — said alarm was rising on Embassy Row and among their home governments that Trump’s return could mean not just the abandonment of Ukraine but a broader U.S. retreat from the continent and a gutting of the Atlantic alliance.

“There is great fear in Europe that a second Trump presidency would result in an actual pullout of the United States from NATO,” said James Stavridis, a retired four-star Navy admiral who was NATO’s supreme allied commander from 2009 to 2013. “That would be an enormous strategic and historic failure on the part of our nation.”

Formed after World War II to keep the peace in Europe and act as a bulwark against the Soviet Union, NATO evolved into an instrument through which the U.S. works with allies on military issues around the world. Its original purpose — the heart of which is the collective-defense provision, known as Article V, that states that an armed attack on any member “shall be considered an attack against them all” — lives on, especially for newer members like Poland and the Baltic States that were once dominated by the Soviet Union and continue to fear Russia.

The interviews with current and former diplomats revealed that European officials were mostly out of ideas for how to deal with Trump other than returning to a previous playbook of flattery and transactional tributes.

Smaller countries that are more vulnerable to Russian attacks are expected to try to buy their way into Trump’s good graces by increasing their orders of U.S. weapons or — as Poland did during his term — by performing grand acts of adulation, including offering to name a military base Fort Trump in return for his placing a permanent presence there.

At this point in the campaign, Trump is focused on the criminal cases against him and on defeating his Republican primary rivals, and he rarely talks about the alliance, even in private.

As he maintains a broad lead in his campaign to become the Republican nominee, the implications for America’s oldest and most critical military alliance are not clearly advertised plans from Trump, but a turmoil of widely held suspicions charged with unknowability.

Ukraine

Amid those swirling doubts, one thing is likely: The first area where Trump’s potential return to the White House in 2025 could provoke a foreign policy crisis is for Ukraine and the alliance of Western democracies that have been supporting its defense against Russia’s invasion.

Helping Ukraine stave off the attempted Russian conquest has become a defining NATO effort. Ukraine is not a NATO member but has remained an independent country because of NATO support.

Camille Grand, who was NATO’s assistant secretary-general for defense investment early in the war, said that how Trump handled Ukraine would be the first “big test case” that Europeans would use to assess how reliable an ally — or not — he might be in a second term.

“Will he throw Zelenskyy under the bus in the first three months of his term?” Grand, now at the European Council on Foreign Relations, asked, referring to Ukrainian President Volodymyr Zelenskyy.

Trump has repeatedly declared that he would somehow settle the war “in 24 hours.” He has not said how, but he has coupled that claim with suggestions that he could have prevented the war by making a deal in which Ukraine simply ceded to Russia its eastern lands that President Vladimir Putin has illegally seized.

Zelenskyy has said Ukraine would never agree to cede any of its lands to Russia as part of a peace deal. But Trump would have tremendous leverage over Ukraine’s government. The United States has supplied huge quantities of vital weapons, ammunition and intelligence to Ukraine. European countries have pledged the most economic assistance to Ukraine but could not make up the shortfall if America stopped sending military aid.

Some of Trump’s congressional allies, who have followed his lead in preaching an “America First” mantra, already oppose sending further military assistance to Ukraine. And in a broader sign of waning support, Senate Republicans last week blocked an emergency spending bill to further fund the war in Ukraine after demanding unrelated immigration policy concessions from Democrats as a condition of passing it.

But even if Congress appropriates further aid, Trump could withhold delivery of it — as he did in 2019 when trying to coerce Zelenskyy into announcing a criminal investigation into Joe Biden, the abuse-of-power scandal that led to Trump’s first impeachment.

Against that backdrop, Russia’s battlefield strategy for now appears to be biding its time; it is carrying out attacks when it sees opportunities to tie up Ukrainian forces but is not making paradigm-shifting moves or negotiating, officials said. That stasis raises the possibility that Putin has calculated he could be in a much better position after the U.S.’ 2024 election.

‘Everybody owes us money’

Trump likes to brag that he privately told leaders of NATO countries that if Russia attacked them and they had not paid the money they owed to NATO and to the United States, he would not defend them. He claimed at a rally in October that after he had declared that “everybody owes us money” and was “delinquent,” he made that threat at a meeting, and “hundreds of billions of dollars came flowing in.”

That story is garbled at best.

There was a spending-related dispute, but it was over Europeans’ meeting their spending commitments to their own militaries, not money they somehow owed to NATO or to the United States. They did increase military spending during the Trump administration — although by nowhere near the amounts Trump has claimed. And their spending rose significantly more in 2023, in response to Russia’s invasion of Ukraine.

But Trump’s exuberance for retelling his story, coupled with his past displeasure with NATO, is giving fresh alarm to NATO supporters.

Pressed by The New York Times to explain what he means by “fundamentally reevaluating” NATO’s mission and purpose, Trump provided a rambling statement that contained no clear answer but expressed skepticism about alliances.

“It is the obligation of every U.S. president to ensure that America’s alliances serve to protect the American people, and do not recklessly endanger American blood and treasure,” Trump’s statement read.

Some Trump supporters who are pro-NATO have argued that Trump is bluffing. They said he was merely looking to put more pressure on the Europeans to spend more on their own defense.

“He’s not going to do that,” Sen. Lindsey Graham, R-S.C. and a Trump supporter, said of the prospect of Trump’s withdrawing from NATO. “But what he will do is, he will make people pay more, and I think that will be welcome news to a lot of folks.”

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Robert O’Brien, who served as Trump’s final national security adviser, echoed that view.

“President Trump withdrawing from NATO is an issue that some people in D.C. discuss, but I don’t believe it’s a real thing,” O’Brien said. “He understands the military value of the alliance to America, but he just feels — correctly, I might add — like we’re getting played by the Germans and other nations that refuse to pay their fair share for their own defense.”

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But John Bolton, a conservative hawk who served as national security adviser from 2018 to 2019, wrote in his memoir that Trump had to be repeatedly talked out of withdrawing from NATO. In an interview, Bolton said “there is no doubt in my mind” that in a second term, Trump would withdraw the United States from NATO.

As a legal matter, whether Trump could unilaterally withdraw the United States from NATO is likely to be contested.

The Constitution requires Senate consent to ratify a treaty but omits procedures to annul one. This has led to debate about whether presidents can do so on their own or need lawmakers’ authorization. There are only a few court precedents regarding the issue, none definitive.

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Decisions to revoke treaties by President Jimmy Carter in 1978 and by President George W. Bush in 2001 led members of Congress to file lawsuits that were rejected by courts, partly on the grounds that the disputes were a “political question” for the elected branches to work out. While the legal precedents are not perfectly clear, both of those presidents effectively won: The treaties are widely understood to be void. Still, any attempt to withdraw from NATO would likely invite a broader challenge.

In reaction to Trump’s threats, some lawmakers — led by Sen. Tim Kaine, D-Va., and Sen. Marco Rubio, R-Fla. — put a provision in the annual National Defense Authorization Act, which Congress is likely to vote on this month. It says the president shall not withdraw the United States from NATO without congressional approval. But whether the Constitution permits such a tying of a president’s hands is also contestable.

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And European diplomats say that even if Trump were to nominally keep the United States in NATO, they fear that he could so undermine trust in the U.S.’ reliability to live up to the collective-defense provision that its value as a deterrent to Russia would be lost.

A transactional attitude

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The uncertainty stemming from Trump’s maximalist and yet vague rhetoric is bound up in his past displays of consistent skepticism about NATO and of unusual solicitude to Russia.

As a candidate in 2016, Trump rattled NATO allies by saying that if Russia attacked the Baltic States, he would decide whether to come to their aid only after reviewing whether they had “fulfilled their obligations to us.” He also repeatedly praised Putin and said he would consider recognizing Russia’s illegal annexation of Crimea.

As president in July 2018, Trump not only nearly withdrew from NATO at an alliance summit but also denounced the European Union as a “foe” because of “what they do to us in trade.” He then attended a summit with Putin, after which he expressed skepticism about the idea that the United States should go to war to defend a tiny NATO ally, Montenegro.

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With no prior experience in the military or government, Trump brought a transactional, mercantilist attitude to interactions with allies. He tended to base his views of foreign nations on his personal relationships with their leaders and on trade imbalances.

Trump particularly disliked Angela Merkel, the former German chancellor, and often complained that German automakers were flooding America with their products. His defenders say his anger was in some ways justified: Germany hadn’t been meeting its military spending commitments, and over his objections, Merkel pushed ahead with a natural gas pipeline to Russia. Germany only suspended that project two days before Russia invaded Ukraine.

Trump’s allies also point out that he approved sending anti-tank weapons to Ukraine, which President Barack Obama had not done after Russia seized Crimea in 2014.

Still, in 2020, Trump decided to withdraw one-third of the 36,000 U.S. troops stationed in Germany. Some were to come home, as he preferred, with others redeployed elsewhere in Europe. But the following year, as Russia built up troops on Ukraine’s border, Biden canceled the decision and added troops in Germany as a show of support for NATO.

A supportive movement

If he returns to power, Trump will be backed by a conservative movement that has become more skeptical of allies and of U.S. involvement abroad.

Anti-interventionist foreign policy institutes are more organized and better funded than they were during Trump’s time in office. Those groups include the Center for Renewing America, a Trump-aligned think tank that published a paper titled “Pivoting the U.S. Away From Europe to a Dormant NATO,” which provides a rationale for minimizing America’s role in NATO.

On Nov. 1, the Heritage Foundation — a traditionally hawkish conservative think tank that has lately refashioned itself in a Trumpist mold on matters including opposition to aid to Ukraine — hosted a delegation from the European Council on Foreign Relations.

The Europeans exchanged views with ardent nationalists, including Michael Anton, a National Security Council official in the Trump administration; Dan Caldwell, who managed foreign policy at the Center for Renewing America; and national security aides to Sen. J.D. Vance, R-Ohio, and other Trump-aligned senators.

According to two people who attended, Anton told the Europeans he could imagine Trump setting an ultimatum: If NATO members did not sufficiently increase their military spending by a deadline, he would withdraw the United States from the alliance.

As the meeting broke up, Eckart von Klaeden, a former German politician who is now a Mercedes-Benz Group executive, implored Anton to ask Trump to please talk to America’s European allies as he formulated his foreign policy.

That seems like wishful thinking.

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In his statement to the Times, Trump invoked his slogan “America First” — a phrase once popularized by American isolationists opposed to getting involved in World War II.

“My highest priority,” Trump said in the statement, “has always been, and will remain, to America first — the defense of our own country, our own borders, our own values, and our own people, including their jobs and well-being.”