British ambassador Kim Darroch, a seasoned professional who is highly respected in Washington, was embarrassed last weekend by the leak of some of his tough-but-fair assessments of President Trump and his administration in private cables to London. Any other White House would have overlooked the ambassador’s undiplomatic language rather than damage relations with a close U.S. ally. But not Trump, who has turned a minor kerfuffle into a major diplomatic incident by launching a series of crude attacks on Darroch that, on Wednesday, forced him to resign. It’s one more example of the president’s inability to stomach criticism, and of his strange zeal for assailing America’s closest friends.

Darroch, who has observed the Trump administration since it took office, is not a politician but a career diplomat who worked hard to cultivate relations inside and outside the Trump administration. The private reports he dispatched reflected little more than the conventional wisdom about Trump and his policymaking apparatus. Among other things, he said White House decision-making could be “dysfunctional” and “unpredictable,” a fact that any reader of Trump’s Twitter feed is aware of. He described Trump himself as “insecure” – a conclusion that the president just proved with his over-the-top response.

Those who know Darroch are well aware that he is not, as Trump described him, “wacky,” “a very stupid guy” or a “pompous fool.” But even if the ambassador’s reputation is done no damage, the same may not be true of the “special relationship” between the United States and Britain. Not just the outgoing government of Theresa May but also the British political establishment more generally has been shocked by the new low to which Trump has sunk. The head of the British diplomatic service said he knew of no other instance in which the head of a friendly government had announced a refusal to cooperate with a British ambassador.

Boris Johnson, the favorite to succeed May as prime minister later this month, may have damaged himself by declining to publicly defend Darroch or criticize Trump. He could find it harder to sell Parliament and the British public on cooperating with the Trump administration’s priorities, or on the free-trade deal he wants to cut with the United States. And what self-respecting British public servant will now want to serve in Washington, knowing he is subject to being dismissed by a Trump tweet?

Trump is well known for insulting those who criticize him, whether they are Hollywood celebrities or Gold Star families. But he seems to be particularly uninhibited when it comes to close U.S. allies. He appears to care not whether vital relationships with Britain or Germany or Japan are damaged. Yet he has yet to utter a word of criticism, much less direct a taunt, at Vladimir Putin, Xi Jinping or other foreign dictators who are dedicated adversaries of the United States.

We don’t know if Darroch tried to explain that aberrant behavior in one of his cables. But he did write that the Trump administration was unlikely “to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept.” To which we can only say: Right you are, Ambassador.