Officials at the meeting said Trump shocked many present and broke with diplomatic protocol by addressing German Chancellor Angela Merkel by her first name, telling her: "Angela, you need to do something about this".
Merkel, facing domestic political opposition to pushing defence spending up from 1.2 percent of GDP, said she explained to Trump how much was already being done.
But Mrs. Merkel "has benefited at home from Mr. Trump's attacks, since the USA president is deeply unpopular among the German electorate, as he is with voters across much of Western Europe", The Washington Post reported Wednesday.
"He might not like the current president, but I represent the United States", Trump said.
"It's disturbing and even painful to watch, but NATO emerges significantly stronger as a result of Trump's tactics, however unbecoming", said retired Canadian Forces colonel Brett Boudreau, who spent three years at NATO headquarters as spokesman and adviser to the chairman of the NATO military committee.
Trump also lashed out at his longtime nemesis, London Mayor Sadiq Khan, a Muslim who has criticized Trump's ban on travel to the United States from several predominately Muslim countries.
"President Trump never at any moment, either in public or in private, threatened to withdraw from NATO", Macron said.
Instead, he said, "the other 28 allies had agreed to increase their defence spending more quickly to meet a North Atlantic Treaty Organisation target of two percent of their national income within a few years".
THE FACTS: Trump has said this before; it's not true.
"We have this stupidity going on, pure stupidity, but it makes it very hard to do something with Russia because, anything you do, it's like: "Russia, oh he loves Russia", Trump said.
"I'm sorry, they're for White House staff", they were told as they tried to grab vacant seats at the front.
"The president is pretty straightforward about what he believes and he thinks Nord Stream 2 is not in the European Union's best interest and my bet is he'll be more than happy to tell President Putin that straight to his face", said Perry.
NATO Secretary General Jens Stoltenberg was forced to call an emergency budget meeting of all the allies to deal with the staggering demand.
Following an emergency session at the alliance headquarters in Brussels, the United States president said the other members have agreed an unprecedented increase in defence spending.
"I want Trump to come out and say unequivocally "Russia meddled in our election" and I want him to press Putin on that", Jankowicz said.
Speaking at Chequers Friday at the official country residence of the prime minister, Trump said he also would bring up Ukraine, Syria, the Middle East, and nuclear proliferation when he meets with Putin.
"In terms of real capability, the alliance has become stronger over the last couple of years", he said. "So all I can do is say, 'Did you?' and 'Don't do it again'".
He said that the decision to reach two per cent, which had been very hard to achieve in Bulgaria, would be fulfilled in the term of office of the next government, Radev said.