On his way to a summit of NATO leaders, U.S. President Donald Trump undermined the alliance’s core collective defense promise — injecting tension into a gathering designed to keep him interested in European security.

Asked whether the United States remains committed to NATO’s Article 5 clause, Trump told reporters on Air Force One: “Depends on your definition. There are numerous definitions of Article 5. You know that, right? But I’m committed to being their friends.”

“I’m committed to saving lives. I’m committed to life and safety. And I’m going to give you an exact definition when I get there. I just don’t want to do it on the back of an airplane.”

On Wednesday, NATO leaders are expected to formally agree to a new defense spending target of 5 percent of gross domestic product — a sharp increase from the current 2 percent benchmark and something that Trump has been demanding for months.

While NATO Secretary-General Mark Rutte has insisted publicly that the new objective is not designed “for an audience of one,” a private, obsequious message leaked by Trump himself highlights that the gathering’s choreography is mostly designed to provide the U.S. president with a win and to keep him from abandoning the alliance.

“Donald, you have driven us 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, according to a screenshot posted by Trump on Truth Social. “Europe is going to pay in a BIG way, as they should, and it will be your win.”

The NATO secretary-general also congratulated the U.S. president for his “decisive action in Iran.”

Trump also said he spoke to Russian President Vladimir Putin.

Asked aboard Air Force One about the ongoing exchange of long-range missile fire between Iran and Israel, Trump revealed a recent call with the Russian leader and that he was still looking to strike a deal with the Kremlin boss on ending the war in Ukraine.

“As you know Vladimir called me up. He said, ‘Can I help you with Iran?’ I said, ‘No, I don’t need help with Iran. I need help with you.’”

After U.S. and Israeli strikes targeted Iranian nuclear sites, Tehran retaliated with attacks on American assets in Qatar and Israeli positions as well as civilian infrastructure. A tentative ceasefire is now under threat.

Trump also said he would probably meet Ukraine’s President Volodymyr Zelenskyy while in The Hague.