Still, by the time it was over he was ebullient, saying that European allies and Canada had "really stepped up their commitment" - and intimating that his relentless hectoring had forced other allies to spend more than NATO's long-term goal of 2 percent of GDP on defense.
"I'm very consistent. I'm a very stable genius", he said. He pointed to what he said were $33 billion in North Atlantic Treaty Organisation defense spending increases this year as evidence that his push was having an effect.
But, several sources said, Trump instead reopened in strong terms his demand that other countries spend more immediately.
In an apparent swipe at Trump, he added: "Sometimes the corridors, comments and tweets take on more importance than what is negotiated, said or endorsed by heads of state".
And while all member nations have agreed, in principle, to work toward the 2 percent spending goal, each country is ultimately beholden to unique political processes and must consult with their respective parliaments to secure increased military spending.
From left: NATO Secretary General Jens Stoltenberg, Prime Minister of the United Kingdom Theresa May, and U.S. President Donald Trump arrive for a working dinner at The Parc du Cinquantenaire-Jubelpark Park in Brussels on July 11, during the NATO summit.
"Germany is a captive of Russia because it is getting so much of its energy from Russia", Trump said, taking particular aim at the proposed Nord Stream II gas pipeline, which he has previously criticised.
He added that allies had agreed their national plans to get defence spending up to 2 per cent should be "credible".
KELLY: What about this kind of ripple of panic that I gather went through the summit this morning when rumors and reports started flying that Trump might threaten to pull out of the alliance altogether?
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It was a classic Trump performance - bluster, confrontation and demands followed by a unilateral declaration of victory - but his claim was quickly dismissed by the leaders of Italy and France, who disputed they had made any new pledges for increasing spending.
Trump has taken an aggressive tone during the summit, questioning the value of a military alliance that has defined decades of American foreign policy, torching an ally and proposing a massive increase in European defence spending. It was also reported that Trump asked Macron privately to leave the World Trade Organization.
Crimea was annexed from Ukraine by Putin in 2014.
"I'm sorry, they're for White House staff", they were told as they tried to grab vacant seats at the front. "And then today and yesterday, I was probably a little bit more firm".
"I think it is a disgusting thing Germany is doing".
During Trump's meeting with Putin, McCain said, the president "must reverse his disturbing tendency to show America's adversaries the deference & esteem that should be reserved for our allies. That is all", Macron said. "We urge Russian Federation to cease all political, financial and military support to militant groups and stop intervening militarily in the Donetsk and Luhansk regions and to withdraw troops, equipment and mercenaries from the territory of Ukraine".
Trump's attack, including one where he called Germany a "captive to Russian Federation", apparently was a big show, that Trump wanted to do right away, when cameras were on. "And that's fine. Of course, they kill us on trade".
Then, in a head-snapping pivot at the end, he declared the alliance a "fine-tuned machine" that had acceded to his demands to speed up increases in military spending to relieve pressure on the US budget.