LONDON (AP) — Britain's ambassador to the United States resigned Wednesday after being made a diplomatic nobody by President Donald Trump following the leak of the envoy's unflattering opinions about the U.S. administration.

Kim Darroch said he could no longer do his job after Trump branded him a fool and cut off all contact with the representative of one of Washington's closest allies. The criticism came after leaked documents revealed the envoy's dim view of Trump's administration, which he described as dysfunctional, inept and chaotic.

"The current situation is making it impossible for me to carry out my role as I would like," Darroch said in his resignation letter.

In the leaked documents, he called the Trump administration's policy toward Iran "incoherent," said the president might be indebted to "dodgy Russians" and raised doubts about whether the White House "will ever look competent."

"We don't really believe this administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept," one missive said.

British politicians from Prime Minister Theresa May down praised Darroch and condemned the leak, as some accused Boris Johnson, Britain's likely next leader, of failing to stand up for the U.K.'s envoy in Washington because he wanted to curry favor with Trump.

Darroch had been set to retire at the end of the year. It's unclear whether May will have time to replace Darroch before she leaves office later this month. Appointing ambassadors usually involves a formal civil service process with advertisements, applications and interviews, though Simon McDonald, head of Britain's diplomatic service, said the post of ambassador to the U.S. wasn't always chosen that way.

"History shows that there are often bespoke procedures for filling the embassy in Washington, DC," he said.

Though the matter had been brewing for days, Darroch announced his decision the morning after a debate between the two contenders to replace May as party leader and prime minister, Johnson and Jeremy Hunt.

Hunt, who is Britain's foreign secretary, had vowed to keep Darroch in the post, but Johnson pointedly did not.

"I think it's very important we should have a close partnership, a close friendship with the United States," Johnson said.

Darroch's forthright, unfiltered views on the U.S. administration — meant for a limited audience and discreet review — appeared in leaked diplomatic documents that were published in Britain's Mail on Sunday newspaper.

Trump responded with a combined criticism of Darroch fused with a broadside at May, chiding the British leader for failing to get her Brexit deal with the European Union through Parliament.

"I told @theresa_may how to do that deal, but she went her own foolish way-was unable to get it done. A disaster!" Trump tweeted Tuesday. "I don't know the Ambassador but have been told he is a pompous fool."

British officials are hunting for the culprit behind the leak, which was both an embarrassment to May's government and a major breach of diplomatic security.

"We will pursue the culprit with all the means at our disposal," McDonald, the Foreign Office chief, told a committee of lawmakers.

McDonald said it was "vitally important" that ambassadors were able to speak candidly in private and that it was the first time in his career that a head of state has dismissed working with a British ambassador. McDonald told the Foreign Affairs Committee that even hostile states had not taken such action in his nearly 37 years in the department.

"This is not the first time a British ambassador has left post or resigned because of actions against the host government but usually they are governments with whom we have problematic relations rather than friendly relations," Simon said.

But he said the trans-Atlantic relationship was "so deep and so wide that it will withstand any individual squall."

He also said he feared there might be more leaks to come.

Darroch has served as Britain's envoy to Washington since 2016, and the cables cover a period from 2017 to recent weeks. He was a prominent figure in Washington and popular among Trump White House officials, who were always over at the embassy for parties and events.

Trump's tweets caused fury among many British politicians and officials, who found themselves insulted by the president's decision to have the administration cut off contact their ambassador. It underscored that the close relationship between the two countries has become increasingly lopsided — a severe problem at a time the country is preparing to set out a new path with its departure from the European Union.

"It is shameful that Kim Darroch has effectively been forced out for doing the job that diplomats are appointed to do," Scotland's First Minister Nicola Sturgeon tweeted. "Boris Johnson's failure last night to stand up for him — and stand up to the behaviour of Donald Trump — spoke volumes."

Foreign Office minister Alan Duncan went further, accusing Johnson of having "thrown our top diplomat under a bus" for his own personal interests.

But Trump supporter and Brexit Party leader Nigel Farage described the resignation as, "the right decision."

He tweeted: "Time (to) put in a non-Remainer who wants a trade deal with America."