Sources close to the talks told DW's Teri Schultz that Trump demanded European NATO members meet the alliance target immediately, rather than increase spending gradually as agreed to at a previous NATO summit in 2014.
Trump campaigned on a Muslim ban that he later modified to apply to a list of mostly Muslim countries and building a wall on the U.S. Mexico border.
According to diplomats, he plunged the summit into chaos on Thursday by saying that the U.S. would "go it alone", if European states failed to boost their spending to at least 2% by January.
Following the summit, NATO Secretary General Jens Stoltenberg was careful not to contradict the president's claim of a substantial increase in spending but was only able to directly point to members' existing 2 percent commitments. "It confirms the goal of 2 percent by 2024".
He continued the attack Thursday, complaining that, "Germany just started paying Russian Federation, the country they want protection from, Billions of Dollars for their Energy needs coming out of a new pipeline from Russian Federation". As a result, he continued, "NATO is much stronger than it was two days ago".
He dismissed as paltry - "a very small step", the president said - the increases that North Atlantic Treaty Organisation member countries have made in their military budgets in part because of his repeated lectures on the issue, eschewing a victory lap his advisers had encouraged him to take in favor of a sharp slap at allies.
"Indeed, we're increasing it by 70 per cent over the next decade", Trudeau said.
"People are saying, 'He's picking on Germany.' Well, he was", Inhofe said with a chuckle, criticizing the German government for "not even trying to" meet a pledge to devote more to NATO's coffers.
He added: "I've been reading a lot about Brexit over the last couple of days and it seems to be turning a little bit differently, where they're getting at least partially involved back with the European Union".
The US president described himself as a "very stable genius" for securing agreements for extra cash after years of the burden falling on America.
"In that we also defend the interests of the United States".
Trump insisted that he would bring up key subjects including Syria, although he once again failed to rule out recognising Russia's annexation of Crimea. He also said the other leaders had thanked him for raising the issue of how to support NATO's operations.
Also present was France's President Emmanuel Macron, who tried this year to charm Mr Trump into more harmonious transatlantic relationship, only to see the USA president withdraw from the 2015 Iranian nuclear deal and impose tariffs on European goods.
Shelby pointed to the importance of Trump being properly briefed ahead of the sit-downs. I said: "You've got to stop".
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