CNN's John Avlon was stunned by Trump's admission, which he said was unthinkable to imagine any other president saying.
Tusk too urged the Europeans to increase spending as they have promised, but said: "Dear America, appreciate your allies, after all you don't have all that many".
President Trump, pictured above as he departed the White House Tuesday morning on his way to Europe, has repeatedly made clear his disappointment in the attitude to the North Atlantic Treaty Organisation alliance by key partners, and he is expected to be asking tough questions of fellow world leaders Tuesday and Wednesday before departing Brussels for London.
Yet the risk of a blowup is all the greater given Trump's habit of conflating defense spending with trade surpluses, a gripe that puts Angela Merkel and Justin Trudeau firmly in his sights.
"I would like to address president Trump directly who for a long time now has been criticising Europe nearly daily", the former Polish prime minister said. The U.S.is spending many times more than any other country in order to protect them", Trump tweeted Tuesday morning, adding: "Not fair to the U.S. taxpayer. Buried in the Post's article, mostly about Trump's relationship with American allies, are two incredibly troubling paragraphs, based off of claims made by senior White House officials.
Flake also said though he supports getting tough with China, he thinks the United States shouldn't be on its own in that approach. But we can not be taken advantage of.
He said that of the high-stakes meetings of his trip, "Putin may be the easiest of them all".
The meeting will be closely watched to see whether Trump will rebuke or embrace Putin, who has repeatedly denied the allegations of election meddling, in spite of evidence to the contrary. "We lost $151 billion a year ago on trade", the president told reporters.
"It will become increasingly hard to justify to American citizens why some countries continue to fail to meet our shared collective security commitments", Trump said in a letter addressed to Norwegian Prime Minister Erna Solberg seen by Bloomberg News. In the past few weeks, Trump has sent sharply worded letters to the leaders of several European countries, including Germany, Italy and Norway, and also to Canada, warning that the US was losing patience.
"Nobody in Europe can understand why in the world the president would pick fights with his allies here with those who need to be with us when we confront China", he added.