President Kolinda Grabar-Kitarovic mounted a charm offensive at the summit, presenting Trump with a Croatian soccer jersey as giving him plenty of attention. Instead, Trudeau's announcement prior to the summit - plans to lead a new training mission in Iraq and an extension on its role with a North Atlantic Treaty Organisation battle group in Latvia through 2023 - were aimed at demonstrating a commitment beyond mere dollars.
Mr Trump said he told counterparts on Wednesday that he was "extremely unhappy" with the lack of progress being made towards meeting the alliance target of spending 2% of GDP on defence.
The emergency session came amid reports that Trump had threatened to leave the pact if allies didn't immediately up their spending, but officials said no explicit threat was made. His meeting with Russian President Vladimir Putin in Finland next week is generating widespread concern.
He also insisted that Germany must treat Mr Trump "with a mixture of respect and self-confidence".
Trump claimed member nations had agreed to significantly boost their defence budgets and reaffirmed - after days of griping that the USA was being taken advantage of by its allies - that the US remains faithful to the accord.
Since then eight of the 29 allies have managed to achieve the 2 per cent level, and a majority have budget plans to reach it by 2024.
Mr Trump said he didn't want Russian Federation to be a threat, while adding that his meeting with Mr Putin next week "may be the easiest on his Europe trip".
Trump has arrived in Britain, where the government is in crisis over Brexit and where tensions with Russian Federation have spiked after London blamed Moscow for the death this month of a British woman from contact with the Novichok nerve agent.
Leaders had gone into the second day, set to focus mainly on ending the long war in Afghanistan, with low expectations, showing the extent of European frustration with Trump's "America first" policies among the other 28 members of the alliance.
"So I would imagine that's what they will do, but maybe they will take a little bit of a different route". I dont know if that's what they voted for.
It was the most recent in a series of demands and insults that critics fear will undermine a decades-old alliance launched to counterbalance Soviet aggressions.
"Look, we can be competitors", Mr. Gardner added.
Trump repeated demands on the second day of the summit for countries to meet a spending target of two percent of GDP now, instead of by 2024, and to eventually double spending to four percent. "Nato is very important but it's helping Europe far more than it's helping us".
Asked about the mentioned figures of $33 to $40 billion, Trump said that NATO Secretary General Jens Stoltenberg will announce the exact figure, but hinted that the essence was that NATO allies were going to spend those amounts much faster than previously thought.
"He was in a good mood, he said Europe was a continent he appreciated", Luxembourg's Prime Minister Xavier Bettel said of Trump at the evening event, at which leaders enjoyed an acrobatic display and saxophone music in a Brussels park.
"We're protecting Germany, we're protecting France, we're protecting all of these countries".