What did Donald Trump do today?

He threw a tantrum and rage-quit the NATO summit in London.

Last night, a video clip of the leaders of Canada, France and the UK talking about Trump went viral. In it, Canadian prime minister Justin Trudeau is commenting on Trump's erratic behavior from the day before as the British prime minister Boris Johnson and French president Emmanuel Macron nod along. Trudeau mentioned that something Trump said—possibly his sudden disavowal of pro-democracy protestors in Iran—made Trump's staff's "jaws drop to the floor."

As mockery goes, it was pretty gentle—but Trump is easily enraged by anything even remotely like criticism. The attention the clip got was enough to provoke Trump to quit the summit early, though not before he gave himself a chance to call Trudeau "two-faced."

It's not news to anyone else that world leaders think Trump is dangerous, mentally ill, ridiculous, or easily manipulated—because they've said so. But Trump himself, whose staff works very hard to keep him from seeing news that will upset him, may actually have been caught by surprise.

It's not the first time Trump has stormed out of a conference of America's closest allies. The last time he did so was at the June 2018 G7 summit in Montreal, rage-tweeting insults from Air Force One at Justin Trudeau on his way out.

How is this a bad thing?

• This would be a disturbing lack of emotional control even in a small child.

• A president who lets a temper tantrum get in the way of maintaining America's military alliances is unfit for the job.