Though Trump later contradicted his comments by then promising a great USA trade deal, the president made clear his admiration for the 54-year-old Johnson, who Trump said would one day make a great British prime minister. "And I think she found it maybe too brutal".
"I would have done it much differently", Trump said.
Trump said Queen Elizabeth, 92, was a "fantastic woman", adding: "up close, you see she's so lovely. and she's got a lotta years left".
At Sandhurst, Britain's elite academy where military officers undergo training, Trump watched a display, travelling later in the now customary helicopter to Chequers, the prime minister's country retreat in Buckinghamshire where he and May held talks.
"If they do a deal like that, we would be dealing with the European Union instead of dealing with the United Kingdom, so it will probably kill the deal", Mr. Trump said in the interview.
Although only a few Tory MPs who have publicly called for Mrs May to step down, leading backbench Brexiteers such as Jacob Rees-Mogg and former leader Iain Duncan Smith have made clear they expect the prime minister to change her Chequers proposals to reflect their concerns.
BBC reporter Frankie McCamley posted footage on Twitter of Mr Trump, dressed in black and wearing a white cap, waving at protesters in the distance as they shouted "No Trump, No KKK, No Racist USA!"
Antoine Griezmann hails diversity of World Cup winning side
Or at least so coach Zlatko Dalic thought. "What we've had in terms of luck over the tournament, we lacked that today". The two previous finals were 0-0 after 90 minutes before being settled with a single goal deep into extra time.
Tears as Thai cave boys learn of hero Navy Seal's death
The soccer teammates had become trapped in the cave June 23 and were finally extracted by experienced divers over three days. Jessada said the boys were under the close watch of psychiatrists and psychologists when informed of the news about Saman.
Palestinian teenager killed in Gaza border protests
Egypt is now engaging in diplomatic efforts to reach a ceasefire but that possibility remains uncertain. The army said protesters attacked soldiers with grenades, bombs, Molotov cocktails, and rocks.
Johnson, the face of the Brexit campaign for many has remained silent in public since he warned in his resignation letter on July 9 that the "Brexit dream" was being suffocated by needless self-doubt.
"I believe as commander in chief he has an obligation to address it and, frankly, put Putin and any other foreign nation that seeks to undermine our democracy on notice that the actions will not be tolerated", California Secretary of State Alex Padilla, a Democrat, said in an interview this week.
At a news conference with May, Trump repeated his belief that immigration had been "very bad for Europe" and for the United States.
Earlier this week two senior ministers resigned in protest at May's plans for trade with the European Union after Britain leaves the bloc next March.
President Trump also attacked the London mayor, Sadiq Khan, as protests took place in the capital and permission was given for a "Trump baby" blimp to be flown.
"And it enables us to build the new economic and security partnerships we want to see with the European Union".
The President said: "This incredible woman right here is doing a fantastic job, a great job".
A dozen demonstrators have staged a protest picnic on the beach in front of the Trump Turnberry golf resort in Scotland where President Donald Trump is spending the weekend with the first lady.