Sir Kim Darroch has every reason to feel betrayed this morning.
Someone - presumably in London and likely within the Whitehall machine - has hung him out to dry, making one of the pivotal jobs in British diplomacy almost impossible.
And the hunt to find the leaker will come too late to save his relationship with the administration he has so assiduously courted for two and a half years.
When the ambassador phones the White House to discuss Iran policy, or the National Security Council to talk about the Syrian situation, will anyone answer the phone?
The great irony is that almost everyone in this town, even in the West Wing, shares Darroch’s analysis of the dysfunction and chaos in the White House.
But the Trump Administration holds grudges and nurtures grievances.
And doing business with the president’s critics is career-ending.
So those phone calls from the British Residence on Massachusetts Avenue may go unanswered.
The president declared Sunday night, talking of Sir Kim: “We are not big fans of that man and he has not served the UK well...I can say things about him but I won’t bother.”
That appears mild, but is actually brutal.
Sir Kim is the man who has spent the last year of his life organising the president’s recent state visit to the UK.
As I mentioned on News at Ten on Sunday night, I have known Sir Kim for over 20 years, and watched him operate in London, Brussels and Washington.
He is both well-respected by his interlocutors and remarkably straightforward.
His critics will say that he is a believer in the European project - the Nigel Farage line of attack - but if that is a sin then the next British prime minister can close down the entire Foreign and Commonwealth Office.
You do diplomacy because you believe in networks, shared values, and regional and global cooperation.
From the very outset of the Trump Presidency, Downing Street sought to charm, flatter and cajole the new president.
The State Visit was the climax of that “flood the zone” effort.
The Queen herself was deployed to ensure that Trump felt that Britain loved and respected him.
Now that is all in danger.
Questions loom for British diplomacy and for the new prime minister.
Is it better to send a committed Brexiteer to be the next ambassador to the US, someone who will be entirely comfortable schmoozing in the bar of Washington’s Trump International Hotel?
Or is it more critical than ever to put in a candid and experienced diplomat, to show that the professionalism of the Foreign Office will not be compromised by a leaker with an agenda?