What did Donald Trump do today?

He explained his abandonment of the United States' Kurdish allies as only he could.

By the time it was morning in Washington today, Turkey had already commenced airstrikes and a ground invasion of the region of Northern Syria previously controlled by the Syrian Democratic Forces, a Kurdish military organization allied with the United States. Turkey regards the SDF—and the Kurdish ethnic group in general—as enemies. 

By this evening, there were reports of Kurdish fatalities as a result of the assault, including civilians.

This was the predictable (and predicted) consequence of Trump's decision to pull American troops out of Syria. The US-SDF relationship had been mutually beneficial: American troops safeguarded the SDF at virtually no risk to themselves, while the SDF acted as a front-line counter-terrorism force against the Assad regime and fighters allied with the Islamic State. 

Put another way, Trump's debatable claims that ISIS was defeated on his watch—at least in terms of controlling territory—are owed in large part to the work of the SDF.

Genuinely bipartisan outrage at the United States' betrayal of its Kurdish allies followed, forcing Trump to try to explain himself today. It's still not clear why Trump so abruptly gave in to Turkish president Erdoğan's demands—although Turkey does seem to be on the list of countries with suspiciously strong influence over Trump's actions. He began with a statement in which he called the Turkish invasion a "bad idea," but didn't even ask Turkey to pull back.

Later in the day, Trump told reporters that the SDF had been allied with the United States for, he implied, selfish reasons. 

The Kurds are fighting for their land, just so you understand. And somebody wrote a very, very powerful article today. They didn't help us in the Second World War, they didn't help us with Normandy, as an example.

Trump also complained about the cost of supporting the SDF's operations in Syria, which by any standard has been a bargain. When a reporter pointed out that ISIS prisoners that the SDF had been guarding were likely to escape, Trump replied, "Well, they'll be escaping to Europe."

Why does this matter?

• A president who abruptly and without explanation does things that help only America's enemies is unfit to serve, regardless of the reason.

• Presidents should be able to coherently explain why they did what they did.