At a hastily arranged news conference before leaving Brussels, he said, "I let them [NATO members] know that I was extremely unhappy with what was happening. Every single USA president has been pushing the point of extra spending since Reagan and they have all been played I am not going to be".
He also said meeting the queen would be an experience Trump "will really cherish".
Trump closed out the tumultuous two-day summit by reaffirming the United States' commitment to the almost 70-year-old alliance and signing the joint declaration, despite spending much of the summit berating allies over defence spending and accusing Germany of being beholden to Russia because it buys Russian natural gas. And he claimed the other 28 members had agreed to boost their own defense spending to as much as 4 percent of gross domestic product - a claim that other leaders disputed.
It's a typically Donald Trump approach to diplomacy and getting things done - he likes to sign pieces of paper that are largely symbolic, he attacks allies on Twitter but keeps sweet in person - and he sabre-rattles using the gravitas of the United States to get his way.
During the summit, Trump reportedly broke diplomatic protocol by calling German Chancellor Angela Merkel by her first name, saying "Angela, you need to do something about this", a source told Reuters.
As a strong proponent of diplomacy, I believe a meeting between President Trump and President Putin could be a productive one.
"We are being played for fools", he reportedly told leaders at a meeting meant to revolve around Georgia and Ukraine.
Wallace said he will ask Putin about Russian meddling in the 2016 presidential election and potential meddling in the upcoming midterm elections. "It reaffirms a commitment to 2% in 2024".
As he flew off to the United Kingdom on Thursday for the next leg of his European tour, it was left to President Emmanuel Macron of France to correct the record following Trump's freewheeling press conference in which he claimed to have pushed allies into new defence spending commitments.
The Independent calls Mr Trump's tour "the undiplomatic visit" after the president attacked Mrs May's Brexit plan.
Shortly after criticism, North Atlantic Treaty Organisation leaders promised their "unwavering commitment" to increase defense spending, signing a declaration the states they are "committed to improving the balance of sharing the costs and responsibilities of alliance membership".
Referring to planned protests on Friday, Trump added: "I think he has not been hospitable to a government that is very important".
"He's been very nice to me the times I've met him".
The latest tariffs Trump has proposed, on $200 billion worth of Chinese-made goods, would raise the price of 40 percent of China's exports to the USA and begin to shrink the $375 billion trade surplus Beijing ran in 2017.
The second day of the defence pact meeting was disrupted and repeatedly rescheduled, as Trump's insistence on renegotiating his allies' defence budgets took precedence over issues such as Ukraine and Georgia's vulnerability to Russian Federation.