Trump's Marine One departure from the ambassador's residence was met by jeers from demonstrators banging pots and pans, and another pack of protesters lined roads near the palace. Their signs read: "Dump Trump", "Lock Him Up", "There Will Be Hell Toupee".
From Brussels, Trump heads to England, where May's government is in turmoil over her plans for exiting the European Union.
While Trump said on Thursday that he expects the Helsinki summit to be "just a loose meeting", some at home are hoping it will be a "non-event" with nothing groundbreaking. As representatives from the alliance's 29 member states return to their respective countries - or, in the case of USA president Donald Trump, travel on to meet his Russian and British counterparts - the participants will all be trying to make sense of what happened. "I think 4 percent is the right number".
The outdoor arrival ceremony at Blenheim - Trump wore a tuxedo and first lady Melania Trump a butter-yellow, chiffon off-the-shoulder gown - was a grand affair marked by a military band in bearskin hats, hundreds of business leaders in black tie and gorgeous setting sunlight.
The mood was far less jovial in Belgium earlier in the day.
U.S. intelligence agencies concluded that Moscow interfered and Trump has said he would discuss it, although he has stated both a willingness to believe Putin's denials and USA agencies.
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.
Trump has said next week's meeting with Putin "may be the easiest" part of his European tour.
"President Trump never at any moment, either in public or in private, threatened to withdraw from NATO", Macron said. He said the allies had confirmed their intention to meet the goal of 2 per cent by 2024 and no more.
"Yesterday I let them know that I was extremely unhappy with what was happening", he said.
"Everywhere you look there are these dire predictions: 'It's the end of the Western world, ' and all that", Toomas Hendrik Ilves, who served as President of Estonia from 2006 to 2016, told me on Tuesday over dinner in Tallinn, his nation's capital. They're happy to do it. "And yet, he came into the news conference and declared victory", Bays said. Trump tweeted this morning before the second day of talks.
Asked about pressures on countries with weaker finances, he said, "We have many wealthy countries with us today but we have some that aren't so wealthy and they did ask me if they could buy the military equipment, and could I help them out, and we will help them out a little bit", he told a news conference.
Following the summit, NATO Secretary General Jens Stoltenberg was careful not to contradict the president's claim of a substantial increase in spending but was only able to directly point to members' existing 2 percent commitments.
Trump did not draw a direct link between weapons sales and his efforts to persuade other North Atlantic Treaty Organisation countries to correct shortfalls in defense spending below North Atlantic Treaty Organisation targets, but vaunted the benefits of US -made defense equipment.
German news agency DPA, Politico and The Times London reported the US President had openly threatened that the US would "do our own thing" unless the wealthiest allies were spending 2 per cent of their GDP on defence by January.