Whether you think the U.S. should have had troops in Syria or not, or agree with Trump’s decision to pull them out or not, or agree with his decision to pull them out as and/or when he did or not, this passage, from a story about “our” dealings with the Kurds, is worth dwelling on, and remembering for future reference:

“We thought that America would keep its promises,” said Mr. Abdi, the commander of the Kurdish-led Syrian Democratic Forces. “But in the end there was weakness — and disappointment.”

The United States joined forces with Mr. Abdi’s group five years ago, when it was looking for skilled Syrian fighters who could effectively serve as ground troops for an American air campaign against the Islamic State. As the alliance matured, the United States armed and trained Kurdish-led fighters and pressed them to shift their priorities to serve American interests.

The United States pushed them to take the fight against ISIS to areas outside their traditional homeland, costing them many lives. It also discouraged them from negotiating a deal with the Syrian government, telling them that sticking with the United States would win them a stake in the country’s future.

“We said being associated with the U.S. coalition would put you in a position where you would be represented,” Gen. Joseph L. Votel, former head of the military’s Special Operations and Central Commands, said in a telephone interview. “You’d be on the winning team.”

In an effort to placate Turkey, the United States convinced the Kurds to destroy their defenses, softening them up for a Turkish attack. It also sought their help in the United States’ regional struggle with Iran, a cause they had little stake in.

For the Kurdish-led forces, the sting was not that American troops were withdrawing from Syria, which they knew would happen eventually. It was that after five years of their fighting and dying alongside American troops in the battle against ISIS Mr. Trump pulled the plug so suddenly that they were ill-prepared for what came next.

“It was a stab in the back,” said Nesrin Abdullah, a spokeswoman for the Kurdish women’s militia. “The Americans kept saying they would not allow the Turks to enter, but in the end that’s what happened.”

Yeah, we did that in Vietnam, too. Maybe we should try, in the future, to avoid doing this kind of thing again?