What did Donald Trump do today?

He forgot why he was withdrawing U.S. troops from Syria.

Less than a day after Trump announced via tweet that he was suddenly withdrawing 2,000 U.S. troops from the conflict in Syria, he seemed to forget why he had made the order. His tweet on the subject is confusing, even in context, because no single part of it is true.

This is a lie. Russia has celebrated Trump's decision, in everything from its English-language Twitter account to a personal endorsement from Vladimir Putin. Iran's government has not made a formal statement, but individual Iranian strategists cheered the reduction of American influence in a region where Iran sees itself as the controlling power—a view shared by analysts elsewhere. 

The only Syrians unhappy about Trump's decisions are the ones who had been the United States' allies and protectees.

This is false, although Trump (who is famously attuned to Russian interests, and has gotten confused about which side the United States is on in Syria before) may actually believe it. 

To be clear: Russia, Iran, and the Assad regime in Syria were never fighting the Islamic State with the United States. The United States is on the other side of the conflict. 

This is just silly. The United States has had the "most powerful military in the world" since at least the end of World War II.

22 hours earlier, Trump seemed to think—incorrectly—that ISIS had been defeated in Syria.

Not coincidentally, Secretary of Defense James Mattis resigned today.

Why does this matter?

• This is not the sort of issue that the President of the United States can afford to be confused or compromised about.