BRUSSELS — Donald Trump this week dramatically stepped up his threats toward NATO as his rage at America's allies intensified over their refusal to join the U.S. war against Iran.

On Wednesday the U.S. president said he was “absolutely” considering quitting the alliance. Although he didn't elaborate on that threat in a televised address later that evening, the remarks were his strongest yet in underlining his distaste for the 77-year-old pact. 

“I'll be discussing my disgust with NATO,” he said ahead of his speech, later telling POLITICO: “I’m disappointed in them … if I ever did need them, they wouldn't be there.”

So far, Trump hasn’t taken any steps to walk out — a move that U.S. law forbids him from making without Congressional approval. But Trump’s threats against the alliance, his use of “them” instead of “us” when talking about NATO, and his earlier calls to annex Greenland from ally Denmark, all point to a country that no longer sees itself as an integral part of the alliance it founded.

But what could the U.S. in practice do if it wanted to lend substance to the president’s threats?

POLITICO spoke to nine experts, legal scholars and NATO officials, who described Trump's options as well as how realistic they are, and how damaging they would be for the alliance. Some were granted anonymity to speak freely about sensitive matters.

Scenario 1 — Ramp up the rhetoric

Dialing up the threats, criticism and rhetoric on NATO would continue what Trump is doing now.

The U.S. president has already repeatedly chipped away at NATO’s collective defense clause, known as Article 5, and cast doubt as to whether he would really send U.S. troops to defend the country's allies. Reiterating this week that the alliance was a “paper tiger,” he added that Russian President Vladimir Putin “knows that too.”

European leaders have highlighted this risk.

“Alliances like NATO are valuable because … of the trust behind it,” French President Emmanuel Macron said Thursday. “If you create doubts every day about your commitment, you empty [NATO] of its substance.”

Every time the U.S. president questions the alliance, it “damages severely the credibility of NATO's defense and deterrence posture,” said Gerlinde Niehus, an independent security expert and former longtime NATO official. 

“Deterrence functions also psychologically … in the perception of the brains of your adversary,” she said. “If your adversary thinks you are a paper tiger … then, of course, this is an open invitation to Vladimir Putin and to a degree to [China’s] Xi Jinping to test the alliance.”

Inside the Pentagon, the feeling is that Trump’s threats are more of the same from the longtime NATO-skeptical president. 

Likelihood: 5/5

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Scenario 2 — Act as a spoiler 

Trump could also choose to make life difficult for allies inside NATO without going in all guns blazing.

That’s already happening in a limited way. The U.S. has exploited the fact that all policy documents in NATO working committees are approved unanimously to block reports on softer issues like climate change and human security, sometimes alongside other allies, two NATO diplomats said. Work on the latter topic has effectively “gone to zero,” one of the diplomats said.

Overall, “the U.S. still has a solid team, they participate in committees … they negotiate,” the same diplomat argued, but added that Washington could do more damage if it wanted to by bringing work to a halt in more central committees such as those dealing with Ukraine and Russia.

The U.S. could also refuse to pay its dues to NATO’s common budget covering things like operating expenses. (It currently pays around €800 million, or 15 percent of the total.) But while that would be “disruptive,” Niehus said, “it would not be the end of the world” for other allies to replace that contribution. 

Some inside the Trump administration are reportedly considering imposing a “pay-for-play” model on NATO that would block allies who don't meet their spending targets from having a voice on joint missions and triggering Article 5. While there is “no mechanism” to enforce that strategy, Niehus said, Trump could still achieve it via political pressure.

Speaking on behalf of the organization, a NATO official told POLITICO: “We don’t comment on the details of deliberations among Allies. Discussions in committee are an essential part of NATO’s daily work in which all Allies are regularly engaged.”

Likelihood: 3/5

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Scenario 3 — Withdraw U.S. troops

Washington could also decide to pull its troops from Europe.

The U.S. currently has between 67,500 and 85,000 troops stationed on the continent across at least 31 permanent bases and 19 military sites. Trump has limited maneuverability: Under a 2025 law he must keep 76,000 troops in Europe unless the pullback is shorter than 45 days or he obtains approval from Congress.

If Trump withdrew the legal maximum of roughly 9,000 soldiers, that would be “reasonably” damaging for the alliance but not catastrophic, said Ed Arnold, a senior defense expert at the Royal United Services Institute think tank and a former NATO official. European allies could replace those troops, he said, or match them with equivalent capabilities like long-range missiles. 

Yet that’s unlikely to happen, Arnold argued, because Trump is interested in keeping troops and military assets in Europe to be able to deploy rapidly in conflicts such as the war in Iran.

“If they're looking to expand the war in the Middle East, they're actually quite useful being there because then they can move between theaters,” he said, “so this is where the political desires of the president meet the actual operational requirements” of the Pentagon.

“You take your troops and also your specialists from where you need … [and] you're actually just going to hurt your own operations.” Arnold said.

Likelihood: 2/5

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Scenario 4 — Soft exit

Trump could also bring the alliance to its knees without formally quitting.

At the less extreme end of the spectrum, the U.S. could pull out of NATO’s four-year military planning cycle, which determines what kit and how many troops each member must assign to the alliance in an invasion scenario, based on three region-specific defense plans.

Doing so technically wouldn’t affect American military commitments, said Arnold, but would effectively freeze them as pledged in the last cycle that ended last year. That would leave Europeans scrambling to plug gaps — including in areas like air defense, intelligence and air-to-air refueling.

The U.S. could also boycott meetings at NATO or withdraw its delegation. That would be “very damaging,” Arnold said, since it would effectively paralyze the alliance’s work given it relies on unanimous decisions.

If Trump wants to be more aggressive, he could also look to the history books. In 1966, French President Charles de Gaulle quit NATO’s integrated command — as Greece did briefly in 1974.

In practice, that would devastate the alliance, Arnold said. Given Washington’s comparatively central role in the alliance, that would likely mean pulling all American troops assigned to NATO and forcing the resignation of the alliance’s top commander, U.S. Gen. Alexus Grynkewich.

So far, European allies aren’t worried about these scenarios, according to two senior NATO diplomats. “If they stop doing things [like] ensure capabilities to NATO, we are in serious trouble,” said one of the senior alliance diplomats, adding it's “not a particular concern” today.

Likelihood: 2/5

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Scenario 5 — Hard exit

Formally leaving NATO comes with difficult legal hurdles: Trump would technically have to win the backing of two-thirds of the Senate to do so before triggering Article 13 of the alliance’s founding treaty — a process that takes one year.

Yet the U.S. president can also quit treaties unilaterally — as he did in 2020 when he left the Open Skies mutual aircraft surveillance treaty. U.S. courts could move to block that, though the judicial branch has often been reluctant to intervene in foreign policy.  

Still, such a move would certainly invite lawsuits from Democrat-led states or U.S. citizens doing business in Europe. Congress could join if either chamber flips after the November mid-term election, said Scott Anderson, a senior editor of Lawfare. 

“It feels to me like judges are less willing to side with him after a year of executive overreach,” said one U.S. defense official.

“President Trump has made his disappointment with NATO and other allies clear,” said White House deputy spokesperson Anna Kelly, “and as the President emphasized, ‘the United States will remember.’”

Yet the prospect of abandoning NATO comes with a stark warning from some allies.

“It is hard to imagine NATO without U.S. participation,” said a third senior NATO diplomat. “So, this should weigh on any such decision Washington does or does not make.”

Likelihood: 1/5

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This article has been updated.

CORRECTION: This article has been updated to correct the amount the U.S. pays into NATO’s common budget. It is €800 million.