British politicians and officials have reacted with outrage to the resignation of their ambassador to the U.S. amid a rift with President Trump over leaked diplomatic cables, with many accusing the President of bullying their government.

The leak on July 7 of classified memos written by Kim Darroch to the U.K. government, in which he called the Trump Administration “inept” and “incompetent”, triggered a slew of personal insults from the President. Trump tweeted that Darroch was “a very stupid guy” and “a pompous fool.” He also disinvited him from an official dinner July 8, saying “We will no longer deal with him.”

Darroch, who had been due to end his four-year term as ambassador in 2020, announced Tuesday morning he would step down early. “The current situation is making it impossible for me to carry out my role as I would like,” he said in a statement.

The resignation caused alarm among British politicians, many of whom expressed concern that a U.S. president’s forcing a change of U.K. diplomatic staff represents a threat to U.K. national sovereignty.

“If we allow ourselves to be bullied in who we choose to represent us, then frankly what does sovereignty mean?” Tom Tugendhat, a lawmaker from the ruling Conservative party and chairman of the government’s foreign affairs committee told Sky News. “If you can’t even choose who represents you, in what way are you in charge of anything?”

Others warned that the resignation reflected Britain’s future place on the world stage after leaving the E.U. “This is a disgraceful example of what “taking back control” truly looks like: pandering to bigoted foreign leaders and letting them dictate the fate of UK ambassadors,” David Lammy, a lawmaker from the opposition Labour party, wrote on Twitter.

“It’s hard to describe just how big a blow to our diplomatic standing in the world this resignation represents,” tweeted Tom Watson, Labour’s deputy leader.

Darroch’s fellow diplomats expressed shock at his treatment by the President.

“I think a lot of us feel very angry about the way that this has turned out,” says Tom Fletcher, a former government adviser on foreign affairs and ambassador to Lebanon. “He’s effectively been bullied out of the job because of a leak and a very insecure U.S. president who resorts to trolling and online bullying of the representative of really close ally. It’s unprecedented.”

“[The U.K. and the U.S] had a number of high level meetings lined up today and I assume what happened was that the White House made clear that [Darroch] shouldn’t be at those meetings,” Fletcher tells TIME. “I think in the end he took one for the team.”

Fletcher says he could only recall similar situations occurring in countries with whom the U.K. has a very different relationship. “In Zimbabwe, [Robert] Mugabe used to be very critical of individual high commissioners, I think. In Syria, Bashar Al Assad, at various moments was very critical of individual ambassadors and tried to get them replaced. But that’s not the kind of company that we imagined our closest ally to be. It’s bad company.”

Peter Ricketts, a former head of the U.K. Foreign Office and a former ambassador to France, tweeted that Darroch had “been taken out by an act of political sabotage.”

Before his resignation, lawmakers and diplomats had widely defended Darroch’s comments, with outgoing prime minister Theresa May saying it was an ambassador’s job to provide the U.K. government “an honest and unvarnished view” of foreign administrations – despite disagreeing with the comments themselves.

But Boris Johnson – the man who will almost certainly become Britain’s prime minister when his Conservative party’s leadership race concludes in July – had refused to explicitly support Darroch, dodging a question about the dispute in a televised debate Tuesday night.

Some lawmakers condemned the likely future leader for failing to stand up to Trump.

“[Johnson] has thrown our top diplomat under the bus…to serve his own personal interests.” Alan Duncan, a Conservative government minister, told the BBC.

Emily Thornberry, a Labour lawmaker, said in a statement that Johnson’s response was a “humiliating, servile, sycophantic indulgence of the American president’s ego to go unchallenged.”

Johnson told reporters Wednesday that he “regrets” Darroch’s resignation, calling him “a superb diplomat” and calling for the leaker of his diplomatic cables – who has not yet been identified – to be “eviscerated.”

The choice of Darroch’s replacement will be one of the first matters on the next prime minister’s desk, Fletcher says. “Whoever it is will have a much much harder job now. They’ll be more wary of how to do their job and more vulnerable,” he says. “We’re in uncharted waters.”

Write to Ciara Nugent at ciara.nugent@time.com.