What did Donald Trump do today?

He threatened a war crime.

Trump issued a bizarrely specific threat to Iran via Twitter today:

Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have.........targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD.

There is almost certainly no such list of 52 targets—or at least not one that actual military commanders will take seriously in the event of further hostilities. The United States military does not draw up attack plans based on numerical symbolism.

No matter what Trump says, it is extremely unlikely that American military personnel will follow any order to attack sites "important to Iranian culture." Not only would this almost certainly involve attacking civilians directly—a war crime—it is also a war crime to target sites of cultural significance. In fact, the most recent UN resolution on the subject passed the Security Council with U.S. approval while Trump was president.

Even in much more serious military conflicts than the one Trump is trying to provoke with Iran, the United States military has a proud history of respecting and attempting to preserve culturally significant sites in warfare.

Why does this matter?

• Attacking civilian targets for their cultural significance is what terrorists do.

• The honor and integrity of the United States is more important than the president's need to act tough.

• This doesn't make Trump or the United States look strong.