US President Donald Trump has arrived in the UK for the start of a four-day visit, during which he will meet with UK Prime Minister Theresa May as well as with Queen Elizabeth II during a weekend in Scotland.
While Mr Johnson may now be a backbencher, Mr Trump said he hoped he would still see the former foreign minister - another blow to the fragile position of Mrs May.
Anti-Trump protesters with critical signs were lining the roadway leading to the palace near Oxford.
Labour Party legislator Paul Flynn, who has criticized Trump in Parliament, says Trump has outraged Britons - and people around the world - with his harsh treatment of immigrants.
"So that was the full planning that went into it - 10 pints of stout and, you know, late-night conversation."
"There is definitely a sense that Britain needs America more because of Brexit", said Bronwen Maddox, head of the Institute for Government, a think tank. Vince Cable, the leader of the pro-EU Liberal Democrats, said, "Most of us don't think he is particularly good judge on Brexit or anything else".
Opponents to the controversial U.S. leader have threatened mass protests but Mr Trump is expected to avoid areas such as central London where demonstrators are likely to gather.
The comments come after May suffered a series of resignations from her Cabinet after she signalled that Britain was heading for a softer form of Brexit with closer ties to the European Union than previously expected.
Ambassador Johnson sought to play down Trump's comments.
Asked in Brussels about the massive demonstrations expected at the next stop of his European trip, Mr. Trump said it was "fine" that there were protests planned.
Ahead of Mr Trump's visit, Mrs May said that when the United Kingdom leaves the European Union "there will be no alliance more important in the years ahead".
After London, he will travel to Scotland and then onto Helsinki to meet with Russian president Vladimir Putin.
But there are still plenty of detractors, as loudly demonstrated by a passenger in vehicle driving past the United States flag-adorned pub who shouted "F*** Trump", to which Mr Smyth chuckled.
"It's also an opportunity to tear down the bureaucratic barriers that frustrate business leaders on both sides of the Atlantic".
Only one person, the digital entrepreneur and philanthropist Baroness Martha Lane-Fox, has publicly refused the invitation.
Air Force One lands at Stansted Airport.
On Friday, Mrs May and Mr Trump will go to watch a joint counter-terrorism exercise by British and USA special forces at a military base.
The two leaders will hold talks the following day at Chequers, the 16th-century manor house which is the prime minister's official country residence.
One person missing at the palace dinner, though, will be the queen, who will be hosting the president and first lady for tea at Windsor Castle on Friday afternoon.