Alienating allies is bad enough. Now President Donald Trump is abandoning one, and the military and moral consequences could be catastrophic.

In what appears to be just the latest phone call with a foreign leader that has “horrified” White House aides, Trump told Turkish President Recep Tayyip Erdogan on Sunday that the U.S. would redeploy 100-150 troops who had been working closely with U.S.-backed Kurdish forces, paving the way for Erdogan to “soon be moving forward with its long-planned operation in Northern Syria,” according to a White House statement.

The Kurdish forces are part of the Syrian Defense Forces (S.D.F.), whose sacrifices against ISIS are one of the key reasons for the terrorist group’s battlefield losses. (ISIS ideology is far from dead, however, which worries more responsible U.S. officials.) The S.D.F. is also detaining tens of thousands of ISIS fighters and their families, an essential role that may end if it needs to redeploy personnel to respond to a Turkish incursion.

Erdogan has long sought to establish a Northern Syrian “safe zone” that would be 20 miles deep along a 300-mile stretch of the Syrian-Turkish border. Erdogan plans to repatriate up to one million refugees there, despite international organizations warning against doing so. But the real reason appears to be to attack the S.D.F., which it links with the Kurdish-separatist P.K.K., which Ankara considers terrorists.

U.S. national security officials have been stalwart in their support of the S.D.F, whose troops have died defending American objectives. When Trump announced a since-scuttled plan to withdraw U.S. forces from Syria in 2018, Defense Secretary James Mattis resigned in protest, as did his top envoy in the fight against ISIS, Brent McGurk.

In a series of tweets, McGurk was withering in his criticism. “The WH [White House] statement tonight on Syria after Trump spoke to Erdogan demonstrates a complete lack of understanding of anything happening on the ground,” McGurk wrote, delineating the errors, including the fact that the U.S. is not holding any ISIS detainees. They are being held by the S.D.F., McGurk wrote, “which Trump just served up to Turkey.”

McGurk’s strong statements reflect other foreign policy leaders assessment of U.S. foreign policy, which former Secretary of State Colin Powell, a Republican, recently characterized as in “shambles.” Trump’s former U.S. ambassador to the United Nations, Nikki Haley, tweeted her criticism, too.

And key lawmakers found rare bipartisan consensus in rejecting Trump’s impulsive decision. One of Trump’s key Senate allies, South Carolina Republican Lindsey Graham, took a moment out from defending Trump from another foreign-policy fiasco — his call to Ukraine’s president — to tweet about working with Maryland Democratic Sen. Chris Van Hollen on a veto-proof bill to impose sanctions on Turkey if its forces invade Syria and that the two “will call for their suspension from NATO if they attack Kurdish forces who assisted the U.S. in the destruction of the ISIS Caliphate.” The decision “to abandon our Kurdish allies and turn Syria over to Russia, Iran, & Turkey will put every radical Islamist on steroids,” Graham wrote, adding that it was a “shot in the arm to the bad guys. Devastating for the good guys.”

Never one to be outdone, Trump furiously tweeted on his policy, including that he was “elected on getting out of these ridiculous endless wars.” (Later, responding to criticism, the president seemed to have second thoughts.)

That may be true. But the way to get out of them is to have willing allies. Which one would want to stick its neck out for the U.S. right now?