Trump’s withdrawal will do worse than that.

It will put thousands of Kurdish lives in jeopardy. It will deepen Tehran’s influence in Syria. It will increase the likelihood of all-out war between Israel and Iran. It will underscore the inefficacy of U.S. sanctions to curb Tehran’s ambitions. It will ratify the wisdom of Vladimir Putin’s decision to intervene on Assad’s behalf. It will strengthen Turkish strongman Recep Tayyip Erdogan’s hand, not only in northern Syria but also in Turkish politics, just as he was finally beginning to experience serious reversals after 16 years in power.

And it will fundamentally jeopardize the gains made against the Islamic State, around 10,000 of whose fighters are in the custody of the Kurdish forces now being attacked. As Mazloum Abdi, the commander of the Kurdish-led Syrian Democratic Forces, told Bloomberg’s Eli Lake, “If we think the Turkish operation will not stop, we cannot fight ISIS anymore.”

Trump thus repeats Barack Obama’s mistake in Iraq of declaring success, pulling out, and creating the security and political vacuums which ISIS, Iran and other bad actors were quick to fill. That alone should have been enough to dissuade this president from pursuing his course.

Except that Trump’s instinctive need to appease dictators appears to be even more powerful than his aversion to imitating his predecessor. Distracting attention from impeachment surely played a role, too, based on the view that ending “stupid endless wars” is generally a political winner — at least until the consequences of our geopolitical fecklessness are again felt fatally at home.

All of which makes it noteworthy that Trump’s Kurdish betrayal has elicited such a political backlash, including among some of his more reliable lackeys in the Republican caucus. People like Senator Lindsey Graham understand that what the U.S. is now doing isn’t simply foreign policy folly. It’s a national disgrace.

It’s a signal that Americans are the friends you never want: there for you when, and only when, it’s convenient for them. It’s evidence that our moral values are tissue paper around the glass fragments of our president’s ego. It’s proof that the idealism that stormed Normandy, fed Europe, democratized Japan, and kept West Berlin free belongs to an increasingly remote past.

It means that American sailor or soldier seen on the horizon is no longer “freedom man.” He’s fair-weather friend.

Even now, this is not how most Americans, including many of Trump’s supporters, would wish to see themselves. People on their way to the bottom have their occasional moments of clarity, seldom seized. In the Syria debacle, Republicans have a chance to see, if not save, themselves.

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips. And here’s our email: letters@nytimes.com.

Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram.