Trump left Washington early Tuesday for Brussels where leaders from the 29 members of the NATO alliance are hoping for a show of unity.
Trump left Washington early Tuesday for Brussels where leaders from the 29 members of the NATO alliance are hoping for a show of unity despite stark transatlantic tensions on a host of issues.
Speaking about his upcoming meetings on his European tour, including his first summit with Putin next Monday in Helsinki, Trump told reporters "frankly, Putin may be the easiest of them all. Who would think?"
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 blocking US imports into the bloc, the world's biggest market.
"It's certainly going to be an interesting time with NATO," Trump told journalists. "NATO has not treated us fairly but I think we will work something out. We pay far too much and they pay far too little."
The meeting of Western leaders in Brussels has the potential to turn into another public bust-up following a divisive and bad-tempered summit of G7 nations in Canada in June.
The summit is seen as one of the most difficult in years amid fears that Trump will turn even more hostile about an alliance that has underpinned European security for 70 years.
With French and German officials urging member states to paper over their differences, European Union President Donald Tusk delivered a blunt message to the US leader on Tuesday, telling him "the US doesn't have and won't have a better ally than the EU."
"I would like to address President Trump directly who for a long time now has been criticising Europe almost daily," the former Polish prime minister told a press conference.
"Dear America, appreciate your allies, after all you don't have that many," he added, before reminding Trump that European troops had fought alongside Americans in Afghanistan following the September 11, 2001 attacks on the United States.
"Please remember this tomorrow when we meet at the NATO summit, but above all when you meet President (Vladimir) Putin in Helsinki. It is always worth knowing who is your strategic friend and who is your strategic problem," he said.
Trump will meet the Russian leader in the Finnish capital on July 16 for their first summit amid an ongoing investigation in the US into possible Trump campaign collusion with Russia.
Many European diplomats fear a re-run of a sequence in June when Trump clashed with Western allies at the G7 summit, calling Canadian prime minister Justin Trudeau "dishonest and weak", then praising North Korean dictator Kim Jong Un as "very talented" at a summit afterwards.
"He chews out the allies then embraces the adversary," one diplomat told AFP recently.
The Kremlin branded NATO a relic of the Cold War ahead of the Brussels summit.
"Our attitude to NATO is well known: it's a product of the Cold War and the confrontation of the Cold War," Kremlin spokesman Dmitry Peskov told journalists.
Trump set the stage for clashes at the NATO summit by writing to around a dozen allies to berate them for lagging on a 2014 pledge to try to spend two percent of GDP on defence by 2024.
Speaking to a cheering crowd at a rally this week, Trump told them that the US would no longer be "the schmucks paying for the whole thing."
New figures published on Tuesday appeared to back up his argument, showing that only seven NATO countries -- Britain, Greece, Latvia, Estonia, Poland, Lithuania and Romania -- would reach the 2.0 percent of GDP spending target in 2018.
But NATO chief Jens Stoltenberg pointed out that military spending had been rising in Europe since 2014 and members were making efforts to meet the 2.0 percent target, particularly Germany, which is often singled out by Trump.
"Germany has plans to increase spending by 80 percent from 2014 to 2024. So also Germany is moving in the right direction but I expect Germany to do more," he told a press conference.
Europe's biggest economy is on course to spend just 1.24 percent of GDP on defence in 2018.