President Donald Trump’s betrayal of the Syrian Kurds, America’s key ally in the fight against ISIS, is his most ignorant and morally bankrupt foreign policy move — so far.

On Sunday, in another reckless phone call, Trump gave Turkey’s President Recep Tayyip Erdogan a green light to attack the Syrian Kurds, our most steadfast ally in the defeat of ISIS. The president then ordered the withdrawal of 50 U.S. troops from the Syrian border who acted as a preventive trip wire dissuading the Turks from invading.

Trump never consulted his own Pentagon or State Department or his Kurdish allies before this snap decision. By Wednesday, the Turks were bombarding Syrian Kurdish towns.

In one feckless move, Trump ensured the revival of ISIS, gifted Iran and Russia — and warned off local forces anywhere from fighting alongside Americans in the future. Why would anyone trust America again after what Trump just did to the Kurds?

What was most stunning was Trump’s ignorance of the Kurds’ central role in defeating the ISIS caliphate, dismissing them as if they were bit players. It was the Kurds who did the heavy fighting in Syria, allied with Christian and some Sunni forces.

The 2,000 U.S. forces then in Syria acted in a critical support capacity, but not on the front lines. The Kurdish-led force lost 11,000 men and women, while U.S. troops sustained only six fatalities.

» READ MORE: Syrian Kurdish women fight on front lines against ISIS | Trudy Rubin

In a visit to Syrian Kurdistan in 2016, I met a 20-year-old female Kurdish fighter who showed me photos of her closest friend who had died in battle. This was Peneber, she said, pointing to a long-haired 19-year-old who looked like someone you’d see on an American college campus. But Peneber died in the fight to defeat ISIS, a defeat Trump constantly brags about.

If not for the Syrian Kurds, the caliphate would still exist — or America would have had to send in thousands more troops.

The betrayal of our Kurdish allies has so upset the U.S. military that just-retired Gen. Joseph Votel, former head of U.S. Central Command (including the Mideast), has gone public. Trump’s decision, he says, “threatens to undo five years’ worth of fighting against ISIS.”

» READ MORE: Trump's green light for Turkey to massacre our Kurdish allies must be countered | Trudy Rubin

Contrary to repeated Trump claims, ISIS is not dead, with thousands of fighters now wearing civvies and biding their time to try a resurgence.

Kurdish-led troops, backed by 1,000 remaining U.S. forces, have been preventing any ISIS revival until lagging international talks finally stabilize the wreckage of post-civil war Syria. The Kurds — not U.S. soldiers — have also been guarding prison camps holding 10,000 ex-ISIS fighters and tens of thousands of ISIS wives and children.

But those Kurdish forces will now head for the Turkish border to protect their cities. This will leave huge swathes of Syria open to ISIS resurgence and prison camps without guards.

An ignorant Trump imagines Erdogan will keep ISIS down and manage those prison camps. “I told President Erdogan it’s going to be your responsibility,” he said Monday. But Turkey has no interest in squeezing ISIS or managing ISIS prison camps. During the war against ISIS, Erdogan refused repeated requests from Washington to close his border to ISIS fighters, who moved back and forth freely.

The Turkish leader has made repeatedly clear he has only one reason for invading Syria — to act out Turkey’s historic enmity toward the Kurds.

Erdogan wants to establish a “so-called” safe zone inside Syria, 20 miles deep all along the Turkish border, which contains most of the Kurdish population. The Turkish leader will likely try to drive the Kurds from their heartland, as he did when Turkey invaded the Syrian Kurdish border town of Afrin in 2018. He will then replace the Kurds with Sunni Arab Syrian refugees, many of them Islamists. Hundreds of thousands of Kurds will be forced to flee into Iraq, becoming refugees.

The scenario is so ugly it has spurred a Republican backlash — including from many senators, Majority Leader Mitch McConnell, and ex-U.N. Ambassador Nikki Haley, and even televangelist Pat Robertson.

Sen. Lindsey Graham, normally a sycophantic Trump backer, tweeted: “Pray for our Kurdish allies who have been shamelessly abandoned by the Trump Administration. This move ensures the reemergence of ISIS.” Graham says he will “lead [an] effort in Congress to make Erdogan pay a heavy price.”

Unless the GOP stands up to Trump, and Trump stands up to Erdogan -- immediately -- that will be too little, too late.

But it is Trump who precipitated this crisis, not Erdogan. And it is Graham and his colleagues who still enable the feckless Trump behavior that led to this deadly debacle.

Gen. Votel did a service by speaking out. Why haven’t we heard from James Mattis, who resigned as defense secretary over Trump’s previous threat to quit Syria, or from H.R. McMaster? (As for Mike Pompeo, he defended Trump’s shameful betrayal).

If our Kurdish allies are slaughtered, all of Trump’s GOP enablers will be complicit in their deaths.