How the King will deal with his trickiest state visit yet

In part, those who work with the King will simply trust his long experience in global diplomacy to get the job done.

“It’s not his first rodeo,” says one source, American pun probably intended.

And for the rest of it, the King is preparing in his own way: at Highgrove, where a sunny weekend will see him out in the garden and holding a large, ring-bound folder full of notes.

He will study every word, insiders say, from the biographies of everyone he will meet – accompanied by their pictures – to a reminder of all his previous visits, and those of his ancestors.

The British and US embassies have provided extensive briefings and there are notes on current affairs for ease, although the King is across those anyway, and background information for each of the 32 engagements he will carry out over six days.

His staff have been planning for the trip “carefully, thoughtfully and optimistically”, one source says.

The King and Queen are travelling at the request of the UK Government, officially to celebrate (or commemorate, from the British perspective) the 250th anniversary of American independence.

In reality, the Royal family has found itself, once again, on a rescue mission.

“These things are never easy,” says a palace source of the trip. “But if they were, it wouldn’t need the King to do it – we could leave it to the politicians.

“It’s the whole point, purpose and power of state visits to have a unique individual making the most of a unique relationship.”