The convention-shredding president had ignored diplomatic niceties ahead of touching down for the four-day visit - his first to Britain since taking power - by rebuking his beleaguered host as she struggles over Brexit.
Trump's criticism comes over the prime minister's new Brexit plan, which was unveiled in full on Wednesday.
Liam Fox, Britain's trade minister, tweeted after the Suninterview was published that it was terrific to hear Trump "talk so positively about UK & US Trade tonight at Blenheim Palace".
"I think whenever his detractors go after him, it makes him double down and it actually encourages him to keep going and prove everybody wrong", she said.
Trump personally criticized May's handling of Brexit, saying that her so-called soft-Brexit approach went "the opposite way" to what he had recommended and that it was "very unfortunate".
A trade deal with the United States is one of the main aims of Brexit supporters within May's Conservative Party, who are concerned that she is making too many concessions to the EU. "I think they agree with me on immigration", he told reporters in Brussels.
In an interview with Britain's Sun newspaper published late on Thursday, Trump said May's plans for a business-friendly Brexit would leave it too close to the European Union to allow a new trans-Atlantic trade deal to be struck.
French Foreign Minister Jean-Yves Le Drian said Friday on BFM television that Trump "can't tolerate that there is an ensemble called the European Union".
The Trumps were greeted in the courtyard of Blenheim Palace in Oxfordshire by UK Prime Minister Theresa May and husband Philip for the dinner in the President's honour.
Some signs at Thursday's protests condemned Trump's immigration policy, demonstrating the global outrage he has drawn for separating families at the U.S. -Mexico border and imprisoning children and babies away from their parents.
President Donald Trump has revealed he feels unwelcome in London and a baby blimp made in his likeness is to blame.
On Thursday night, hundreds of demonstrators chanted outside the U.S. ambassador's residence where Trump was staying on the outskirts of London, providing a preview of the large protests expected on Friday. So I think allowing millions and millions of people to come into Europe is very, very sad.
On Friday, Mrs May and Mr Trump will go to watch a joint counter-terrorism exercise by British and U.S. special forces at a military base.
She listed Mr Trump's immigration policies, bans on some people entering the USA, his foreign policies, and lack of support for taking action on climate change as having affects across the globe.
He also added that Johnson, "would be a great Prime Minister".
It is not simply the protesters, who are expected to dog Trump throughout his visit, including his weekend in Scotland, but his fraught relationship with political leaders accustomed to harmonious exchanges with US leaders, a tradition of unity that goes back at least to the vital World War II partnership of Franklin D. Roosevelt and Winston Churchill.
This is the first time that Mr Trump has visited the United Kingdom as president, despite having held office since 2016.
He is then due to spend two days at golf courses he owns in Scotland before travelling to meet Russian President Vladimir Putin.
The Duchess of Sussex misses Suits
They apparently answered her question by saying that five children for Megan and him was way too many! Patrick J. Meghan played paralegal-turned-lawyer Rachel Zane on the hit series for seven seasons.