By SEUNG MIN KIM

WASHINGTON (AP) — President Donald Trump on Tuesday injected some uncertainty over whether the U.S. would abide by the mutual defense guarantees outlined in the NATO treaty as he headed to its summit — comments that could revive longstanding concern from European allies about his commitment to the military alliance.

“Depends on your definition,” Trump told reporters on Tuesday as he was headed to The Hague, where this year’s summit is being held. “There’s numerous definitions of Article Five, you know that, right? But I’m committed to being their friends.” Asked later to clarify, Trump said he is “committed to saving lives” and “committed to life and safety” but did not expand further, saying he didn’t want to elaborate while flying on an airplane.

The remarks, which came to reporters on Air Force One as Trump traveled to the Netherlands, previewed what could be another volatile appearance by Trump at a summit celebrating an alliance that the Republican president has often derided.

And it comes amid a backdrop of tumult in the Middle East, after Trump moved to strike three nuclear enrichment facilities in Iran as well as the president’s sudden announcement that Israel and Iran had reached a “complete and total ceasefire.” The sharp U-turn in hostilities — followed hours later by Trump’s declaration that both parties violated the agreement — had already started to shape the summit, with NATO Secretary-General Mark Rutte publicly dancing around the issue even as hundreds of people showed up in The Hague on Sunday to denounce the conflict in a protest that was initially focused on defense spending.

Still, other NATO countries have become accustomed to the unpredictable when it comes to Trump, who has made no secret of his disdain for the alliance, which was created as a bulwark against threats from the former Soviet Union.

Trump’s debut on the NATO stage at the 2017 summit was perhaps most remembered by his shove of Dusko Markovic, the prime minister of Montenegro, as the U.S. president jostled toward the front of the pack of world leaders during a NATO headquarters tour.

And he began the 2018 summit by questioning the value of the decades-old military alliance and accusing its members of not contributing enough money for their defense — themes he has echoed since. In Brussels, Trump floated a 4% target of defense spending as a percentage of a country’s gross domestic product, a figure that seemed unthinkably high at the time.

“NATO was broke, and I said, ‘You’re going to have to pay,’” Trump said Tuesday, recounting his initial encounters with the alliance. “And we did a whole thing, and now they’re paying a lot. Then I said, ‘You’re going to have to lift it to 4% or 5%, and 5% is better.’”

That 5% figure is “good,” Trump said, adding: “It gives them much more power.”

Sen. Jeanne Shaheen of New Hampshire, the top Democrat on the Senate Foreign Relations Committee, will also attend the NATO summit this week. She said if Trump does anything to sow division within the alliance, it would benefit Xi Jinping of China, which NATO countries have accused of enabling Russia as it invades Ukraine.

“That does not help America, does not help our national security,” Shaheen said in an interview. “What it does is hand a victory to our adversaries, and for an administration that claims to be so concerned about the threat from (China), to behave in that way is hard to understand.”

Trump heavily telegraphed his attitude toward global alliances during his presidential campaigns.

As a candidate in 2016, Trump suggested that he as president would not necessarily heed the alliance’s mutual defense guarantees outlined in Article 5 of the NATO treaty. And during a campaign rally in 2024, Trump recounted a conversation with another NATO leader during which Trump said he would “encourage” Russia “to do whatever the hell they want” to members who weren’t meeting the alliance’s military spending targets.

In The Hague, Trump will tout the pledge to hike military spending, which requires other NATO countries to invest in their defense at an unprecedented scale. In a private message from Rutte that Trump posted on his Truth Social account on Tuesday, the secretary-general praised him for driving NATO “to a really, really important moment for America and Europe, and the world.”

“You will achieve something NO American president in decades could get done,” Rutte wrote in the message that Trump published, which NATO confirmed he sent. “Europe is going to pay in a BIG way, as they should, and it will be your win.”

Last week, the president went as far as to argue that the U.S. should not have to abide by the 5% spending pledge he wants imposed on the other NATO countries, although he appeared to soften those comments on Tuesday.

That 5% is effectively divided into two parts. The first, 3.5%, is meant to be made up of traditional military spending such as tanks, warplanes and air defense. What can comprise the remaining 1.5% is a bit fuzzier, but it can include things like roads and bridges that troops could use to travel. According to NATO, the U.S. was spending about 3.4% of its gross domestic product on defense as of 2024.

Most NATO countries — with Spain as the key holdout — are preparing to endorse the pledge, motivated not just by Russian President Vladimir Putin’s invasion of Ukraine to bolster their own defenses but also perhaps appease the United States and its tempestuous leader.

“He hasn’t said this in a while, but there are still a lot of worries in Europe that maybe the United States will pull out of NATO, maybe the United States won’t honor Article 5,” said Matthew Kroenig, vice president and senior director of the Atlantic Council’s Scowcroft Center for Strategy and Security and a former Pentagon official. “I think there is a real fear among Europeans that we need to deliver for Trump in order to keep the United States engaged in NATO.”

Kroenig added: “Like it or not, I do think Trump’s tougher style does get more results.”

European allies have taken note of potential signs of a broader U.S. retreat. France and other NATO countries have been concerned that the Trump administration is considering reducing troop levels in Europe and shift them over to the Indo-Pacific, which Cabinet officials have signaled is a higher priority.

Still, Secretary of State Marco Rubio and U.S. Ambassador to NATO Matt Whitaker have underscored the U.S.’ commitment and have said the Trump administration is only seeking a stronger alliance.

The White House has not said which world leaders Trump will meet with at the World Forum in The Hague. Trump said Tuesday that he’ll “probably” see Ukrainian President Volodymyr Zelenskyy. The two leaders were scheduled to meet at the Group of 7 summit in Kananaskis, Alberta, earlier this month before Trump abruptly cut his trip short and returned to Washington as the Israel-Iran conflict was intensifying.

But Trump does get quite the royal treatment this week: He plans to stay Tuesday night at Huis Ten Bosch palace, home to Dutch King Willem-Alexander.

Associated Press writers Mike Corder and Lorne Cook in The Hague, Netherlands, and Darlene Superville in Washington contributed to this report.