Kim Darroch resigned on Wednesday as Britain’s ambassador to the United States after the leak of his candid observations on the Trump administration, a ferocious response from President Trump and the failure of the likely next prime minister, Boris Johnson, to support the British envoy.
Mr. Darroch submitted his resignation in a letter that said the situation was making it impossible for him to carry out his role. “Although my posting is not due to end until the end of this year, I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador,” he wrote.
On Monday, Mr. Trump said the White House would no longer deal with Mr. Darroch after the leak of confidential emails written by the ambassador that had described the Trump administration as “clumsy and inept.” The president described the ambassador as “wacky,” a “very stupid guy” and a “pompous fool,” and called Prime Minister Theresa May “foolish” for ignoring his advice on Brexit.
The dispute has cast a shadow over ties between London and Washington and taken center stage in the Tory leadership contest to succeed Mrs. May as prime minister, which Mr. Johnson is heavily favored to win.
During a televised debate Tuesday night, Mr. Johnson, the former foreign secretary, ignited a firestorm by refusing several opportunities to say that he would keep Mr. Darroch in his post until a scheduled departure date in January. He also declined to criticize Mr. Trump, stressing his good relationship with the White House and playing down the rift.
Within hours, the ambassador had submitted his resignation.
Mr. Johnson’s failure to back the ambassador was met with withering criticism from opponents.
“The fact that Sir Kim has been bullied out of his job, because of Donald Trump’s tantrums and Boris Johnson’s pathetic lickspittle response, is something that shames our country,” said Emily Thornberry, the opposition Labour Party’s shadow foreign secretary. “It makes a laughingstock out of our government.”
She added: “Just imagine Churchill allowing this humiliating, servile, sycophantic indulgence of the American president’s ego to go unchallenged.”
Even Mr. Johnson’s rival in the leadership race, Jeremy Hunt, the current foreign secretary, described Mr. Trump’s comments as “unacceptable” and said during the debate that he would keep Mr. Darroch in his job.
Mr. Johnson said on Wednesday that he regretted Mr. Darroch’s departure, and that whoever leaked the ambassador’s messages should be “run down, caught and eviscerated.”
With Mr. Johnson intent on Britain leaving the European Union in October, the “special relationship” with Washington is of particular importance given that Mr. Tump has promised a trade agreement with Britain.
“I think the reality was that in light of the last few days his ability to be effective was probably limited,” Vice President Mike Pence’s chief of staff, Marc Short, said Wednesday morning in Washington. “So it was probably the right course.”
The controversy surrounding Mr. Darroch’s assessments has struck some members of the diplomatic corps in Washington as a broader peril: As one of his fellow European ambassadors put it, there was little in his cables that could not be found in their own.
Mr. Darroch’s descriptions of the administration as inept and chaotic, of reversed decisions and a mystifying policymaking process, differ little from myriad daily news reports and the findings of the slew of books about Mr. Trump’s tenure.
But a senior American diplomat noted, before Mr. Darroch’s resignation was announced, that the publication of the WikiLeaks trove of 250,000 diplomatic cables in 2010 had a similar result, with the resignation of the United States ambassador to Mexico.
The entire episode has left British diplomats shocked. Simon McDonald, the head civil servant in the British Foreign Office, told a parliamentary committee that he could not think of another example in his 37-year-long diplomatic career of a head of state refusing to deal with a British ambassador. That applied even to countries hostile to Britain, he said.
Equally worrying for some has been the lack of support from Mr. Johnson, amid fears that pro-Brexit politicians want to undermine civil servants and blame them for the country’s failure to leave the European Union as scheduled. Mr. Darroch, who once served as Britain’s top diplomat in Brussels, was one of a number of officials viewed with suspicion by Brexit supporters.
In response to Mr. Darroch’s decision, Mrs. May paid tribute to him in Parliament and said that the whole cabinet had rightly given him its support.
“Good government depends on public servants being able to give full and frank advice. I want all our public servants to have the confidence to be able to do that, and I hope the house will reflect on the importance of defending our values and principles, particularly when they are under pressure,” she said.
Jeremy Corbyn, leader of the opposition Labour Party, said of Mr. Darroch, “the comments made about him are beyond unfair and wrong.”
During his tenure, Mr. Darroch was a constant whirlwind of intelligence collection, political analysis, and outreach to the administration and Congress. He organized lunches and dinners for the parade of British officials who move through Washington, from trade ministers to the chiefs of the British intelligence agencies.
Because he had served as Britain’s national security adviser, Mr. Darroch had especially close ties to the American national security apparatus, and frequently played a key role in coordination on matters involving Iran, Russia and Brexit.
His parties, especially an annual New Year’s party at the Embassy, which is decorated with art from Britain’s museum collections, were among Washington’s most sought-after social events. They sometimes included Trump administration officials, including Ivanka Trump and Jared Kushner, the president’s daughter and son-in-law, both of whom are close advisers to the president.
Yet the ambassador’s access to the highest levels of government waned under Mr. Trump. In past administrations, American secretaries of state were often at the British Embassy.
But neither Rex W. Tillerson nor Mike Pompeo dealt as much with Mr. Darroch, and the National Security Council was not as welcoming a place, even to one of Washington’s most crucial ambassadors, as it had been in previous administrations, Democratic and Republican.
The State Department had no immediate comment on Mr. Darroch’s resignation. On Tuesday, the department’s main spokeswoman, Morgan Ortagus, acknowledged that the controversy had implications for Britain’s internal politics.
“There’s clearly an election going on in the United Kingdom,” she said. “We’re going to stay out of that and we will, of course, let the White House speak for the president’s tweets.”
Ms. Ortagus stressed the importance of the relationship between the two nations.
“We have an incredibly special and strategic relationship with the United Kingdom,” she said. “That has gone on for quite a long time and it’s bigger than any individual; it’s bigger than any government. It’s something that has stood the test of time and will continue to do so.”
Mr. McDonald, the head civil servant in the British Foreign Office, said he had accepted the resignation “with deep personal regret.”
“Over the last few difficult days you have behaved as you have always behaved over a long and distinguished career, with dignity, professionalism and class. The prime minister, foreign secretary and whole of the public service have stood with you: you were the target of a malicious leak; you were simply doing your job.”