The British ambassador to the United States, Sir Kim Darroch, is stepping down from his job after diplomatic cables in which he gave a negative opinion of the Trump administration were leaked, announced the British Foreign and Commonwealth Office.

“Since the leak of official documents from this Embassy there has been a great deal of speculation surrounding my position and the duration of my remaining term as ambassador,” Darroch said in a letter to the Foreign Office. “I want to put an end to that speculation. The current situation is making it impossible for me to carry out my role as I would like.”

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While Darroch noted that his commission didn’t expire until the end of this year, he believes that in the current circumstances the responsible course is to allow the appointment of a new ambassador” to the U.S.

Documents containing Darroch’s critique of the White House were leaked to the Daily Mail on Sunday, which promptly published them. “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,” Darroch wrote in one of the documents, reported the Mail.

While the White House didn’t officially comment on the ambassador’s comments, President Donald Trump quickly took to Twitter to attack Darroch, calling him all sorts of names such as “wacky,” “stupid” and “a pompous fool.” The president also threatened that his administration may “no longer deal” with Darroch.

The ambassador’s longtime colleagues in Britain regretted his departure, with the Permanent Under Secretary at the Foreign and Commonwealth Office, Sir Simon McDonald, saying that Darroch “loyally served the government of the day without fear or favour,” and that he represented “the best of us.”

Prime Minister Theresa May also expressed sadness over the longtime diplomat’s exit, saying, “it is a matter of great regret that he has felt it necessary” to resign.

Even Boris Johnson, the rightist, Trumpesque, frontrunner in the contest to become Britain’s next prime minister, said that whoever had leaked the documents to the Daily Mail “really has done a grave disservice to our civil servants.”