BRUSSELS — President Trump reaffirmed support for NATO on Thursday, but only after stirring more discord with a vague threat that the United States could go its own way if the allies resisted his demands for additional military spending, making a dramatic exit after a summit punctuated by his escalating complaints.
Even as he declared that the American commitment to the trans-Atlantic alliance “remains very strong” ahead of his summit meeting next week with President Vladimir V. Putin of Russia, he continued to assail close partners and further strain diplomatic relations.
In the closing hours of the two-day gathering in Brussels with leaders of the other NATO nations, he forced a last-minute emergency meeting to address his grievances over spending. Then he called a news conference to claim credit for having pressured NATO members to boost their defense budgets “like they never have before.”
That claim was quickly dismissed by the leaders of Italy and France, who disputed that they had made any new pledges for increasing spending, adding to the sense of disarray.
Through it all, possible threats from Russia — and NATO’s plans to keep it in check — hung over the summit meeting, as fears in Europe have risen over Mr. Putin’s increasing assertiveness.
On Thursday, Mr. Trump dismissed concerns that his relationship with Russia was too cozy, or that his hardball tactics at NATO had played into the hands of Mr. Putin, whom he is to meet in Helsinki, Finland, next week. But after 48 hours of overt conflict with allies — and the second international summit in two months where he has sparred openly with European leaders — he said he looked forward to a positive encounter with the Russian president.
“I hope that we’re going to be able to get along with Russia; I think that we probably will be able to,” Mr. Trump said. “We go into that meeting not looking for so much.”
The White House hastily called the news conference amid reports that Mr. Trump had unleashed a tirade at a closed-door morning meeting against member countries he complained were still not spending enough on their militaries. Mr. Trump used the news conference to hail himself, again, as a “stable genius,” saying he deserved “total credit” for pushing the allies to increase their military spending by more than previously agreed to.
According to a person briefed on the meeting, Mr. Trump told other NATO leaders that if their countries did not meet the 2 percent standard by January, the United States “would go it alone,” a comment that some interpreted as a threat to withdraw from the alliance. (Other news reports quoted diplomats who said the president used slightly different wording — saying that he would “do my own thing,” — but he was not specific about what he meant in either case.)
The contentious session prompted NATO leaders to convene a closed-door emergency session to discuss burden sharing within the alliance, and Mr. Trump emerged at the news conference to declare himself the victor.
Mr. Trump sidestepped questions about whether he had threatened to abruptly leave the alliance, and said, “I think I probably can, but that’s unnecessary,” because, he said, member countries “have stepped up today like they’ve never stepped up before.”
“The United States was not being treated fairly, but now we are,” Mr. Trump said. “I believe in NATO. I think NATO’s a very important — probably the greatest ever done.”
But Mr. Trump then quickly turned to asserting that the United States shouldered “probably 90 percent of the cost of NATO.” American contributions actually represent about 67 percent of all military expenditures by alliance members.
The United States pays 22 percent of NATO’s budget, which covers things like offices, salaries and some equipment used in joint operations. According to the International Institute for Strategic Studies, of the $603 billion that the United States spends on the military each year, about $31 billion goes to Europe.
NATO members have pledged to devote at least 2 percent of gross domestic product to military spending by 2024. But Mr. Trump, after berating alliance countries for failing to meet a target that is six years away, then abruptly said Wednesday that they must do so immediately, and the figure should in fact be 4 percent.
As Mr. Trump boarded Air Force One and flew to London for the next leg of his European trip, he left allies struggling to explain what had transpired. President Emmanuel Macron of France said that the meetings were “active and demanding,” but he rejected Mr. Trump’s assertion that the NATO member countries had agreed to anything that was not already in place. Prime Minister Giuseppe Conte of Italy sounded a similar theme.
“A communiqué was issued yesterday,” Mr. Macron said. “This communiqué is clear. It reaffirms the 2 percent by 2024 commitments. That’s all.”
Mr. Conte said, “Italy inherited spending commitments to NATO, commitments that we did not change, so no increase in spending.”
Mr. Macron added that the meeting ended with a stronger alliance because of Mr. Trump’s reaffirmation of his commitment to it.
Asked whether Mr. Trump had threatened to leave NATO, Mr. Macron said, “Generally, I do not comment on what goes on behind the scenes, but at no moment did President Trump — neither bilaterally nor multilaterally — say that he was intending to leave NATO.”
Mr. Trump himself said, “It all came together at the end, and yes, it was a little tough for a little while.” He added, “But ultimately, you can ask anybody at that meeting, they’re really liking what happened over the last two days.”
Buoyed by what he considered to be his achievements at NATO, Mr. Trump also previewed his plans for his meeting with Mr. Putin. He said he would discuss the extension of one nuclear arms control treaty and violations of another, and might broach the topic of possibly stopping military exercises in the Baltics, a goal of Mr. Putin’s. He evaded a question about whether he would recognize Russia’s annexation of Crimea in 2014.
Instead, he blamed his predecessor, Barack Obama, for the annexation, saying, “President Obama allowed that to happen. That was on his watch, not on my watch.”
Mr. Trump said that, after a weekend in Scotland at Turnberry — a golf course and Trump business that he plugged in the news conference as “magical” — he would go “to a pretty hot spot” to meet with Mr. Putin.
Asked to characterize his relationship with the Russian president, Mr. Trump referred to Mr. Putin as a “competitor,” not an enemy, adversary or friend, and tried to wave off expectations that the “loose meeting” with the Russian president would result in a substantive policy outcome.
“It could lead to something very productive,” Mr. Trump said, “and maybe it’s not.”
When asked if Mr. Putin presented a security threat, Mr. Trump offered a grudging compliment: “Hey, I don’t want him to be. And that’s, I guess, why we have NATO.”