Mr Tusk also said that the U.S. did not and would not have a better ally than the EU, reminding the president that it was European troops who had fought and died in Afghanistan after the 11 September 2001 attacks on the US. The think tank was referring to the pledge at NATO's 2014 summit meeting that members would "aim to move toward" spending at least 2 percent of gross domestic product on defense by 2024. At a subsequent rally in Montana last week, the president declared, "Our allies in many cases were worse than our enemies".
Trudeau, who was called "weak" by Trump after the G7 meeting, pledged to boost Canadian troop numbers 540, from around 450 now.
Only eight of the 29 NATO members are expected to reach the target of spending 2 percent or more of their GDP on their armed forces this year, NATO Secretary General Jens Stoltenberg said in February.
"I have the United Kingdom, which is in somewhat turmoil, and I have Putin", Trump said.
The unpredictable Trump's affinity for the leaders of NATO's 28 other members carries the potential to further blur the lines between who is a friend and who is a foe.
"Is the President just going to focus on defense spending and basically hijack the entire conversation?" says Heather Conley, director of the Europe Program at the Center for Strategic and International Studies. And the USA ranks 18 in refugees taken in due to Mideast instability as a percentage of total population, with Turkey, Sweden and Norway accepting the most.
Many US presidents have urged European governments to spend more on their militaries. "Europe far more than it does the U.S".
Trump, who has also questioned the USA military presence in Asia, is challenging those assumptions. "On top of this the European Union has a Trade Surplus of US$151 Million with the USA, with big Trade Barriers on USA goods. NO!" Speaking about solidarity, I want to dispel the American President's argument, which says that the U.S. alone protects Europe against our enemies, and that the United States is nearly alone in this struggle.
"So Congress will have to act to get the President of the United States to implement the sanctions against the man that invaded Crimea and meddled in our elections?" He added that if Trump is warmer toward Putin than the leaders of the military alliance that was founded to protect Europe from Soviet threats, it would go "a long way to undermining NATO, undermining the trans-Atlantic relationship, undermining our relationship with our allies".
James Comey, the former Federal Bureau of Investigation director, said of Donald Trump that he bore more resemblance to a mob boss than a democratic politician.
A country's defense contribution shouldn't be measured only as a percentage of GDP, but also in terms of troops and hardware, she said in an interview with Bloomberg Television in Berlin.