The G-7 summit ended with Trump lashing out at the other members and threatening to stop all trade with them if they didn't change their practices. In a tweet from Air Force, Trump suggested he may demand those nations "reimburse" the United States. "But above all, when you meet President Putin in Helsinki".
Trump arrived in Belgium amid the soccer-mad nation's World Cup semifinals match vs. France.
In a startling public outburst, Trump told NATO Secretary-General Jens Stoltenberg that Germany was wrong to support a new $11-billion Baltic Sea pipeline to import Russian gas while being slow to meet targets for contributing to NATO defense spending that was meant to protect Europe from Russia. Smith, who served as a national security advisor for then-Vice President Joe Biden, said Trump does not seem to understand the amount planning it takes for some of these governments to expand their budgets.
"But we can not be taken advantage of", Trump added.
Trump will meet the Russian leader in the Finnish capital on July 16 for their first summit amid an ongoing investigation in the U.S. into possible Trump campaign collusion with Russia. "I hope you have no doubt this is an investment in our security, which can not be said with confidence about Russian & Chinese spending". He called Putin a "competitor".
He adds: "I think that getting along with Russian Federation, getting along with China, getting along with others is a good thing, not a bad thing".
"NATO countries must pay MORE, the United States must pay LESS".
After the summit, Mr Trump will travel to Britain for a state visit but, more concerning for Brussels, he will host his first one-on-one summit with Mr Putin in Helsinki on July 16.
As Mr Trump carried out his verbal assault on Europe, Nato Secretary-General Jens Stoltenberg instead looked to appease Mr Trump, thanking him for his "leadership" in pushing for greater defence spending even as the president attacked allies ahead of the summit.
Trump's tweets would likely set a combative tone for the upcoming meetings.
Trump's weeklong trip to Europe will continue with a stop in Scotland before ending with a sit-down in Helsinki with Putin, whose country the USA intelligence community has concluded interfered in the 2016 election to help Trump win.
President Donald Trump's four-nation European tour has allies fretting over the risk of damage he could do to the decades-old North Atlantic Treaty Organisation alliance.
Trump's relationship with Putin, and his inconsistent stance on Russia's interference in the 2016 United States presidential election, is perhaps one of the most scrutinized aspects of his presidency.
Besides Brussels, Trump's trip will also take him to London, where Prime Minister Theresa May's government is in turmoil over her plans for exiting the European Union.
Eight NATO allies will reach the benchmark by the end of the year, and 15 are on the track of meeting the target by 2024, according to a recent statement by the White House.