Asked whether he thought Putin was a friend or foe, Trump said he couldn't say, adding that he sees the Russian leader as a "competitor".
During a rally last week in Montana, Trump vowed that he would "tell NATO: 'You've got to start paying your bills."' The president also bemoaned that Americans were "the schmucks that are paying for the whole thing".
Trump refuses to label Putin a foe, an adversary, an enemy, despite his past and current attacks on the US electoral system.
On Nato, President Trump's main objection is that a number of member states have not increased their defence budgets to the target of 2% of economic output.
And despite Trump's outward rhetoric, the US contribution hasn't gone down, suggesting that nervousness around the summit may be overplayed, said Michaels. "'And it means a lot more to you than protecting us because I don't know how much protection we get by protecting you'". The NATO chief said that the Europeans and Canada are projected to spend around US$266 billion more on defence by 2024.
Trump loathes Germany's trade imbalance with the United States and feels the country is free-riding off the US security umbrella.
On July 16, President Trump will travel to Helsinki, Finland to meet with his Russian counterpart, Vladimir Putin.
Trump's tweet on Tuesday echoed earlier posts on Twitter on Monday and his criticism at a rally of supporters in the United States last week, in which he said that Washington was unfairly carrying nearly all the cost of defending Europe. The U.S.is spending many times more than any other country in order to protect them.
Leaders converged on Brussels fearful of what the combative USA president might say or do to rupture the liberal world order, with some European diplomats privately predicting calamity. Recent and ongoing North Atlantic Treaty Organisation missions include bolstering defenses against Russia's aggressive posture along the alliance's eastern border; leading the 41-country-strong stabilization operation in Afghanistan; the counter-ISIS mission in Iraq and Syria; anti-terrorist activities in the Mediterranean Sea region; anti-piracy missions to secure vital shipping routes in the Gulf of Aden off the African coast, enhancing cybersecurity measures among allies; and supporting humanitarian and peacekeeping missions, which at one time included delivery of 189 tons of relief supplies for Americans affected by Hurricane Katrina in 2005.
"The president was willing to offer concessions to Kim without getting anything specific or concrete in return", said Jeffrey Rathke, deputy director of the Europe Program at the nonpartisan Center for Strategic and International Studies. "Charge us big Tariffs (& Barriers)!"
Trump's weeklong trip to Europe will continue with a stop in Scotland before ending with a sit-down in Helsinki with Putin.
"As far as I'm concerned, a competitor", he noted, adding that it would be good to get along with Russian Federation and China.
Trump's victory in the 2016 presidential election shocked British diplomats in Washington and relations between May and Trump have been strained at times. 'I'm confident the UK-US alliance will play a leading role in advancing our shared values of democracy and freedom, ' he said.