"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."

The publication of those words will likely end Sir Kim Darroch's tenure as Britain's ambassador to the United States. It comes from one of numerous diplomatic cables leaked to the Daily Mail, and the words make Darroch's position untenable.

Not that this is exactly fair to Darroch. Like all British ambassadors, he expected his words to be read only by top officials in London. And London expects its ambassadors to deliver candid cables that can inform more effective policy. But the damage is done.

Upon entering office later this month, Britain's new prime minister will likely replace Darroch. To keep him in Washington would be to risk Britain's most important foreign relationship for the sake of one ambassador.

Again, however, this is regrettable. Darroch is a smart representative of British interests who would have expected to serve one or two more years in his most prestigious post. Yet the leak has aggravated President Trump, who has condemned Darroch. Theresa May is now doing damage control, desperately trying to cool Trump's fury.

Meanwhile, given the president's well-known personal sensibilities, it's quite obvious that whoever leaked these cables had an agenda. I'd guess that it's either a very unpatriotic idiot in the U.K., or a Russian or Chinese or other hostile intelligence service. There is simply no rational excuse as to how someone in the British government could think these leaks would do anything but damage British and American interests.

Nevertheless, Britain simply cannot afford to alienate the leader of its closest ally. The U.K.'s diplomatic, military, intelligence, and $60 billion annual export relationship with America is its foreign policy keystone. In the context of economic and political doubts over Brexit, the strength of that relationship matters now more than ever.

So as I say, when either Boris Johnson or Jeremy Hunt enters office on July 24, expect replacing Darroch to be an early order of business. Indeed, for the sake of an alliance he cares deeply about, Darroch may even request a different posting before then.