WASHINGTON ― President Joe Biden on Tuesday praised the NATO alliance at its 75th anniversary celebration as he potentially became the last U.S. president to address the group’s annual summit.

Biden told the civilian and military leaders from 32 countries assembled in Washington that the alliance, founded after World War II to keep the peace in Europe and thwart Soviet expansionism, has a new mission in stopping Russian dictator Vladimir Putin’s invasion of Ukraine.

“Today NATO is more powerful than ever ― 32 nations strong,” he said at evening ceremonies at the Andrew Mellon Auditorium, where the founding treaty was signed in 1949, as he welcomed the two newest members, Sweden and Finland.

“Our commitment is broad and deep,” he said. “Our nations will continue to keep faith in what we pledged in years to come.”

How long the United States will honor that pledge, though, is unclear. Donald Trump, the coup-attempting former president who will become the Republican presidential nominee next week to challenge Biden’s reelection, has long threatened to abandon NATO.

According to his own defense secretary, Trump planned to pull out of the alliance in his second term ― a plan foiled by his loss to Biden in the 2020 election.

John Bolton, his former national security adviser, said Trump had wanted to withdraw in his first term and almost did at the summit in 2018. Bolton said Trump never understood how NATO worked and did not care to learn.

“He spent four years as president, he didn’t know anything about it when he entered the Oval Office, and he didn’t know anything about it when he left,” Bolton said in an interview earlier this year.

Trump confirmed Bolton’s analysis on Tuesday with a post on his social media platform, once again mischaracterizing how the organization functions, describing it more like a mob protection racket than a military alliance.

“When I became President, I noticed that there were only 7 of the 28 Countries, that were then Members, who were paid up. Most Members were delinquent, some having paid very little, if anything. I found this unacceptable, and insisted that they pay if they wanted the protection of the U.S.,” Trump wrote.

In fact, member countries have no meaningful “dues.” Rather, the nations’ militaries work together in a common defense, which has been invoked only a single time: when NATO joined the U.S. war against the Taliban in Afghanistan after the Sept. 11, 2001, terrorist attacks in the United States.

In 2014, after Russia invaded Crimea, the NATO allies agreed that every nation would increase its military budget to at least 2% of its gross domestic product by 2024. Trump, despite being corrected by his military advisers, repeatedly claimed that European nations were cheating the U.S. and were “delinquent” in their payments, even though there have never been such payments.

Biden on Tuesday noted that when he took office, only nine nations were hitting their 2% commitment but that the number now stood at 23. He attributed that increase to the work of Jens Stoltenberg, the retiring secretary general, whom Biden awarded the Presidential Medal of Freedom on stage.

“Today NATO is stronger, smarter and more energized than when you began, and a billion people across Europe and North America, indeed the whole world, will reap the rewards of your labor for years to come,” Biden said.

Although Biden told the audience that Americans appreciate the work of NATO, it is nevertheless unclear what anyone could to do to stop Trump from unilaterally withdrawing from the treaty if he is elected and chooses to do so, as presidents have sweeping power in international affairs. It is also unclear whether NATO could survive without the United States for the four years of a second Trump presidency ― or longer if he chooses not to leave office at the end of it.

Trump two months ago was convicted of 34 felony counts for falsifying business records to hide a hush money payment to a porn actor ahead of the 2016 election. He faces three other criminal prosecutions as well, which in all expose him to decades in prison if convicted.

Despite this, he handily won the GOP presidential primary and is currently leading in polls to defeat Biden in November.