'We are protecting Germany, we are protecting France, we are protecting all of these countries and then numerous of the countries go out and make a pipeline deal with Russian Federation where they are paying billions of dollars into the coffers of Russian Federation.
The Trump administration has tried to compete with Russia in the energy sector in Europe, but relies on shipping tankers of natural gas and oil, which a pipeline like the German-Russian Nord Stream 2 would likely undercut. Their concerns had already set in ahead of Trump's arrival on the continent, following weeks during which the US President has increasingly and vociferously aired out his grievances against many of them.
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. I get along with her very well, I have a very good relationship.
Mr Stoltenberg - apparently startled by the ferocity of the United States president's assault - shot back as he reminded Mr Trump of NATO's common cause.
Trump is scheduled to meet Merkel at the summit later Wednesday and with Russian President Vladimir Putin in Helsinki on Monday.
Mr Trump, in a message to Germany, asked why the USA should "protect you against Russia" when the two countries were making deals. "After all, you don't have that many".
"Germany is captive of Russia because it is getting so much of its energy from Russia", Mr Trump said. Other presidents has raised European defence spending levels in the past but he is intent on dealing with it.
Some alliance members have privately voiced concern that Trump might also pull out of a major upcoming military exercises, including one, Trident Juncture, scheduled for October.
Mr Trump said he had not spoken with Mrs May, adding: "Boris Johnson is a friend of mine". In recent weeks, various European leaders have also threatened to retaliate against US tariffs and filed complaints to the World Trade Organization.
"We're protecting Germany, we're protecting France, we're protecting all of these countries".
"So, we're going to have a meeting on that and the secretary general has worked very hard on that, he understands the problem and hopefully we can get it resolved". "We're not going to put up with it, we cant put up with it", he said. "Who would think", the president said.
Of his meetings in Brussels and Britain and with Putin, he said: "Frankly, [the meeting with] Putin may be the easiest of them all - who would think?"
Mr. Tusk's challenge to the president appeared more reflective of the European Union than of Poland, where Mr. Trump is relatively popular and leaders are lobbying for a major US military presence in their country.
Crucially, they do not include Germany, Europe's biggest economy and prime target for Trump's invective, which is on course to spend just 1.24 percent of GDP on defence in 2018.