What did Donald Trump do today?

He threw a temper tantrum because someone called him insecure.

Last week, the British tabloid The Daily Mail reported on leaked internal memos written by the British Ambassador to the United States, Kim Darroch. They were harsh in their assessment of Trump. Darroch said that Trump was "inept," desperately insecure, and that his administration was "dysfunctional." He advised other British diplomats talking to Trump to "make your points simple, even blunt," so that Trump could keep up.

Darroch concluded that the situation was not likely to improve, and that Trump's presidency might well  "crash and burn" and end in "disgrace and downfall."

The release of the cables was indeed embarrassing for the British government—but not because Darroch had said something he shouldn't. A spokesperson for the Foreign Office said, "The British public would expect our ambassadors to provide ministers with an honest, unvarnished assessment of the politics in their country. Their views are not necessarily the views of ministers or indeed the government. But we pay them to be candid."

Today, Trump responded to the charge that he was insecure by tweeting this:

I have been very critical about the way the U.K. and Prime Minister Theresa May handled Brexit. What a mess she and her representatives have created. I told her how it should be done, but she decided to go another way. I do not know the Ambassador, but he is not liked or well........thought of within the U.S. We will no longer deal with him. The good news for the wonderful United Kingdom is that they will soon have a new Prime Minister.

In reality, Trump does know Darroch, having met him "seven or eight times" as of last year in the normal course of business. (It's very possible that Trump is unable to remember.)

Realistically, Trump probably could force Darroch out of his job. The problem is that Trump has already shown that he doesn't understand what ambassadors do, which is to serve their own country's best interests. Shortly after taking office, Trump told the British government (via tweet) to appoint his political ally Nigel Farage as ambassador, apparently in the belief it was his choice to make. The response was a flat "no."

UPDATE, July 9: Trump continued to lash out at "the wacky Ambassador" on Twitter today, again insisting (and perhaps believing) that he had not met and worked with Darroch on many occasions. Trump's own comments are starting to do damage as British politicians, including one of the likely candidates to replace Theresa May as Prime Minister, reacted angrily to his treatment of Darroch.

Why is this a bad thing?

• The US-UK relationship is much, much more important than Donald Trump's feelings.

• Throwing a tantrum in public because someone said you were insecure and slow-witted is a pretty good way of proving them right.

• It's really important that presidents understand the basics of diplomacy.