What did Donald Trump do today?

He triumphed in negotiations over himself.

Trump didn't impose a wildly unpopular tariff on Mexico, and spent time today on Twitter insisting that "everyone" was "very excited" by this. 

In theory, Trump was going to "punish" Mexico with the tariff because he felt it wasn't doing enough to protect the United States from Central and South American refugees. (In reality, of course, a 5% tariff on Mexican goods is a 5% sales tax paid by American consumers of Mexican products.) 

But it quickly became obvious that the new "agreement" consists almost entirely of things that Mexico was already doing before Trump's latest tariff threat. As the New York Times put it:

It was unclear whether Mr. Trump believed that the agreement truly represented new and broader concessions, or whether the president understood the limits of the deal but accepted it as a face-saving way to escape from the political and economic consequences of imposing tariffs on Mexico, which he began threatening less than two weeks ago.

Bluffs like this are a pretty common Trump tactic, although not one he's had any real success with. He's threatened several times to close the Mexican border to legal traffic, which would be catastrophic for all concerned, but has always backed down. Even his attempt to militarize the Mexican border was an empty threat: the National Guard troops he summoned ended up doing non-border related maintenance work, and state governors recalled many of them anyway.

Why is this a bad thing?

• You can't govern by stunt.

• It's bad if other countries have no real reason to take the President of the United States seriously.