But it's not simply the protesters, who are expected to dog Mr. 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.
On the planned protests, the ambassador said that Trump appreciated free speech and dismissed as "irrelevant" a giant balloon of Trump depicted as a crying baby in nappies which will fly next to the British parliament on Friday.
"When we leave the European Union we will begin to chart a new course for Britain in the world and our global alliances will be stronger than ever", May said ahead of Trump's visit.
Then, Trump will head to Scotland for a few days.
Meanwhile, a poll by YouGov covering 1,648 respondents has said that 77 per cent of Britons had an unfavourable take on the American president, an incumbent whose one-and-year tenure so far has seen more controversies than not, the AFP report said. It was during that trip to Washington that she invited him to the UK.
And if the President makes an impromptu appearance at the Trump Arms?
After a North Atlantic Treaty Organisation summit where he provoked a crisis session to force allies to raise their defense spending, Trump landed in Britain having described the closest US ally in Europe as being in turmoil over Brexit.
This week's stop will be categorized as a "working visit" - without the elaborate trappings such as a horse parade or a state dinner at Buckingham Palace.
The first couple departed Tuesday for a trip to Europe, where the president is expected to visit the United Kingdom, attend the North Atlantic Treaty Organisation summit in Brussels, and meet with Russian President Vladimir Putin in Helsinki.
Mr Smyth said he hoped the protests, and specifically the Trump baby blimp, do not upset the American public.
"Boris Johnson's a friend of mine, he's been very nice to me, very supportive and maybe I'll speak to him when I get over there".
Trump's trip is the latest installment of the "special relationship" the U.S. and United Kingdom share, which has been a decades-long diplomatic and political bond.
Immediately after arriving in London, Trump and his wife will attend a black-tie dinner in Oxfordshire hosted by Prime Minister Theresa May.
He said: 'I am going to a pretty hot spot right now with a lot of resignations'.
On Friday, Mrs May and Donald Trump will hold bilateral talks at Chequers after which the President and First Lady will travel to Windsor for an audience with the Queen.