And he vowed not to be "taken advantage" of by the European Union, which he accuses of freeloading by relying on the United States for its defence while restricting U.S. imports into the bloc, the world's biggest market.
Trump said on Wednesday that Germany was a "captive" and "controlled" by Russia because of the country's dependence on Russian gas, which is set to increase with the construction of a new pipeline. After all, the US team failed to make it to the World Cup finals.
NATO Secretary General Jens Stoltenberg applauded Canada and European allies Tuesday for having reversed years of cuts by investing more in defence and contributing more troops and equipment to collective security - even as he pushed back against suggestions the alliance was in trouble.
"The notion that America First Trump so obviously supports Brexit and one of its populist proponents is bound to give real pause for a lot of people, who are likely to conclude that if it's that great for the US, then it will be at the expense of the U.K". Germans wouldn't agree with that.
"Officials like Mattis and US Ambassador to NATO Kay Bailey Hutchison have tried to reassure NATO allies, but I think that reassurance is wearing thin", Goldgeier told reporters on Tuesday. He said the pipeline arrangement goes back to 2002 "when everybody viewed Russian Federation in a benign way".
"I think that getting along with Russian Federation, getting along with China, getting along with others is a good thing, not a bad thing", Trump added before leaving for Europe. On Tuesday, European Council President Donald Tusk delivered a stern warning to the USA president: "Dear America, appreciate your allies".
The resignation came just weeks ahead of Wednesday's summit, highlighting Trump's policies are not only dividing United States allies, but also senior U.S. officials.
Trump said Tuesday he "can't say right now" if Putin is a friend or foe, but called him a "competitor".
"After 2 percent, we'll start talking about going higher", Trump said. "We're reflecting that in a resolution that we're bringing to the floor today", said House Speaker Paul Ryan, R-Wis., on Wednesday.
Merkel said it was "completely impossible" to meet the commitments by January in the crisis session that Trump himself later publicly described as "tough for a while".
Prior to boarding Air Force One for Europe, Trump already took jabs at European allies by other tweets, including "NATO countries must pay MORE, the United States must pay LESS".
"The United States is paying far too much and other countries are not paying enough, especially some". His working assumption is that America's trading partners need the USA more than America needs them.
"That's the reason why they agreed to invest more in defence back in 2014", Stoltenberg said.
"Like in football, fair play and team spirit is what we need more than ever", Michel said in an apparent jab at President Donald Trump who keeps questioning why Washington must carry such a heavy financial burden in defense of the West.
That's not how the spending works.
Earlier, President Trump suggested the North Atlantic Treaty Organisation allies should reimburse the U.S for defense costs. Last year's summit was also held in Brussels, making Belgium one of only two countries he will have visited twice. This, for Trump, is the "art of the deal".
THE FACTS: There's no question US military spending constitutes well over a majority of the alliance's overall spending on defense. After spending $3.4 billion on that initiative last year, the Trump administration has proposed boosting it to $6.5 billion in the 2019 budget year.
He will travel to most of those meetings by helicopter, meaning he can likely avoid the large-scale protests in central London, including a giant "Baby Trump" blimp.
Trump, who later arrived at NATO's new billion-dollar headquarters in his presidential limousine, appeared to substantially overstate German reliance on Russian energy and to imply the German government was funding the pipeline, which Berlin says is a commercial venture.