Could Trump follow through on his threats to quit NATO? Experts say it's possible

President Donald Trump arrives for a press conference after the plenary session at the NATO summit in The Hague, Netherlands, Wednesday, June 25, 2025. (AP Photo/Markus Schreiber)

OTTAWA — U.S. President Donald Trump’s comments to a British newspaper this week revived speculation about whether he is ready to pull the U.S. out of the NATO defensive pact, of which Canada is a member.

Venting his frustration over what he claimed is the failure of allies to help America in its war against Iran, Trump told the Daily Telegraph NATO is a “paper tiger” and that the U.S. leaving the alliance is now “beyond reconsideration.”

Aaron Ettinger, associate professor of political science at Carleton University, said the threat of the U.S. quitting NATO has grave implications for Western security and must be taken seriously.

“We can’t just treat Trump’s threats as a TACO Tuesday situation,” Ettinger said, referring to the acronym “Trump Always Chickens Out,” which describes the president’s pattern of issuing aggressive threats before caving or doing nothing.

“NATO depends on the United States and that makes the threat of abandonment, legal or material, a very real prospect.”

According to the most recent NATO annual report released last week, America accounted for 60 per cent of allies’ combined nominal defence expenditures.

While it remains unclear how serious the president is about withdrawal, experts say there are a number of ways Trump could go about removing the U.S. from the alliance — or wrecking it from within.

Pulling out of NATO would be straightforward but not obstacle free — thanks in part to Trump’s own Secretary of State Marco Rubio.

How Trump could try to leave the alliance

Ettinger, an expert in on U.S. foreign policy, said it’s legally possible for Trump to withdraw. The process is clearly outlined in the NATO Charter: any member can leave by simply giving one year’s notice.

But Trump still would have to contend with U.S. lawmakers, the courts and the Constitution.

The president is bound by domestic law in the United States, which for a few years now has stated the president cannot withdraw from NATO without first consulting Congress and winning two-thirds support from the U.S. Senate.

“It would be a real fight that would probably end up at the Supreme Court,” Ettinger said.

Trump would face U.S. legal hurdles

That 2023 law restricting the president’s ability to quit NATO was introduced by Rubio, who at the time was a Florida senator.

In a December 2023 social media post that went viral this week, Rubio wrote that “no U.S. president should be able to withdraw from NATO without senate approval.”

Ettinger said that law means any attempt to leave NATO likely would lead to a Supreme Court challenge and years of litigation. He said constitutional law would lean toward supporting Rubio’s law because Congress supported it.

At the same time, the U.S. Supreme Court is dominated by conservative judges who frequently side with Trump.

Withdrawing not the only option

Wendy Gilmour of the Conference of Defence Associations think-tank said Trump has proven he can be very disruptive and could cause the alliance serious headaches without formally withdrawing from the treaty.

“He is prepared to use executive orders, even when they are not prima facie legal,” she said, noting Trump could draw down or remove U.S. support for various NATO activities.

“It is in the alliance’s interest and in America’s interest to take a deep breath to understand where our interests lie and to figure out a way to address the global strategic instability that has been caused by the U.S. and Israel deciding to attack Iran.”

University of Ottawa international affairs professor Roland Paris suggested Trump could starve NATO of funding and other contributions to the point where it would have about the same effect as walking away.

“He could effectively withdraw the United States from NATO, even if it was not a formal decision, by removing U.S. military participation in NATO, including by withdrawing the supreme allied commander, which is by tradition an American position,” Paris said.

“There would be significant pushback in Congress. He does have the power to unilaterally reduce America’s participation in the alliance. We’re not there yet (but) I wouldn’t put anything beyond him.”

Ottawa’s response: We stand by NATO

Asked if Canada has a backup plan if Trump pulls out of NATO, Foreign Affairs Minister Anita Anand only underscored Canada’s deep commitment to the alliance.

“We are continuously and consistently ensuring that our decisions relating to collective defence are made in the context of this multilateral organization,” Anand told The Canadian Press, noting that Canada just met a key NATO financial commitment of spending two per cent of GDP on defence.

“We are four-square, consistently operating within the NATO framework.”

Why is the White House lashing out now?

Trump was not the only top U.S. politician to cast doubt on the future of the alliance this week.

U.S. Secretary of Defense Pete Hegseth declined to reaffirm support for the alliance at a Tuesday press conference.

“You don’t have much of an alliance if you have countries that are not willing to stand with you when you need them,” Hegseth said, adding Trump is “simply pointing that out.”

Speaking on Fox News this week, Rubio said “unfortunately” the administration must “re-examine” whether the alliance is “still serving its purpose” or becoming a “one-way street” where America has to defend Europe but member nations won’t come to America’s aid.

Both cabinet members added any decision would be up to Trump.

Spain, Italy and other NATO members denied the U.S. military the ability to use their airbases as the country wages war on Iran.

Spain’s prime minister has called the war illegal and unjust, while Italy’s parliament needs to approve such airbase use.

Legal experts have raised concerns about violations of international law, citing the destruction of civilian infrastructure by American airstrikes. Trump also has threatened to bomb civilian installations such as desalination facilities, which produce drinking water — which would constitute a war crime.

Despite floating the prospect of leaving NATO this week, Trump opted against slamming the alliance Wednesday in his prime time television speech on the war — even though Trump had said he would.

He did, however, urge allies to use their militaries to capture the strategic Strait of Hormuz.

Kyle Duggan, The Canadian Press