Since the start of Syria’s civil war, Turkey has taken in 3.6 million refugees, more than any other nation by far.

Now it wants to send many of them back, to resettle in the border zone that Turkey is in the process of seizing from Syria.

“Our goal is to settle at least 1 million Syrian brothers and sisters in our country in this safe zone,” the Turkish president, Recep Tayyip Erdogan, told members of his political party on Thursday.

The obvious problem: Syria is home to nearly 2 million Kurds, and they are concentrated in the north. For the refugees in Turkey to move in, the Kurds would likely have to move out, at the point of a bayonet.

“How are you going to move 1 million people in when people already live there?” asks Henri Barkey, a former State Department official and director of the Middle East Program at the Woodrow Wilson International Center for Scholars.

We are talking about ethnic cleansing on a massive scale. The betrayal of Kurdish fighters who lost 11,000 men and women in the battle against ISIS is bad enough. The coming horrors for Kurdish civilians are likely to be worse.

As it happens, New Jersey has two members of Congress with special insight. Rep. Tom Malinowski (D-7th) served in the Obama State Department and sits on the Foreign Affairs committee. Rep. Mikie Sherrill (D-11th) was a Navy helicopter pilot who served in the Mideast and now sits on the Armed Services Committee.

They are both horrified at the strategic blunder, where most American eyes are understandably focused. But they also are bracing for a humanitarian crisis that’s gotten much less attention, so far.

“We are talking about a massive movement of people,” Sherrill says. “We’ve seen United Nations reports that over 160,000 civilians have been displaced so far. I have great concern and fear for the lives of the Kurds. To say greatly concerned is even an understatement.”

Malinowski was Washington director for Human Rights Watch before moving to the State Department, so he knows something about ethnic cleansing -- the murders, the rapes, the burning of homes.

“It sounds like a sanitary term, but it refers to pushing people off their land, out of their homes, because of their ethnicity or religion,” he says. “And that can only be done with violence.”

Keep in mind, President Trump has effectively given his blessing to all this by moving U.S. troops from the border, giving Erdogan the green light. And nothing in the 13-point agreement that Vice President Mike Pence negotiated with Turkey last week prevents Erdogan from carrying out this plan.

The agreement gives Turkey all it wants. It calls on the Kurdish militias to retreat, and to hand over their heavy weapons and fortification in the border zone. It gives Turkey permanent control of the border zone and promises no sanctions over the invasion. And it lets Erdogan proceed with his grand plan to repatriate 1 million refugees.

“This isn’t a diplomat victory,” says Sen. Chris Murphy, D-Conn. “It’s the capstone of Trump’s abandonment of the Kurds.”

That abandonment weighs heavily on Sherrill, as a vet. She spoke after the invasion with a colleague on the Armed Services Committee, Rep. Jason Crow of Colorado, who fought with the Kurds.

“He said, ‘I have a commitment to them.’ And that’s the feeling we all have,” she says. “We’re talking about U.S. troops on the ground whose backs have been watched by Kurdish troops, fighting side by side with them. So, the reaction in the military, I think morale is incredibly low. A U.S. handshake should mean something.”

The details of this betrayal are almost sickening. This recent summer, the United States tried to reassure Turkey that Kurdish militia groups in Syria presented no threat by asking the the Kurds to blow up tunnels, demolish defensive berms and dig up ammunition caches in the region, which the Kurds reluctantly agreed to do. That left them even more vulnerable.

“You tricked us!” the leader of the Kurdish militia, Mazlum Kobani, told U.S. liaisons, according to the New York Times.

What’s mystifying to Sherrill is that betrayal was so unnecessary. This wasn’t Vietnam, a war that became hopeless even after a decade of intense bombing and the loss of 58,000 U.S. troops. In Syria, the Kurds were doing heavy fighting on the ground against ISIS, while fewer than 1,000 Americans helped with intelligence, training, and air strikes. And it worked, shrinking ISIS to a nub. Now, all that could be lost.

“This is probably the worst decision in the past 50 years, since the Vietnam War,” she says. “We had gotten rid of the physical structures of ISIS and the Kurds had been holding them prisoner. With very little treasure or lives, we had gotten to a much better place. And now this, for no apparent reason. I’m telling you I’m watching Republicans with their heads in their hands. This is not being pushed by the right or the left. What his thinking was is just so unclear.”

Malinowski warns that the human rights catastrophe could extend well beyond the Kurds, given that the Syrian regime now has free reign to pursue its political enemies. As Kurdish families flee southward, he says, Arabs persecuted by the Assad government may be forced to flee northward.

“I’m very worried,” he says. “That would come at a cost of more tremendous human suffering. I don’t see a good way forward right now. All of this was preventable. All it would have required is for the president of the United States to tell Erdogan we would not tolerate this, and we would not move our troops.”

Brace yourself for visions of horror coming from Syria, assuming TV cameras can get near. For the United States, the cost of this mistake is strategic: Our enemies are gaining power in the region, and we are losing it. But for the people of Syria, starting with the Kurds, the price will be far more personal.

More: Tom Moran columns

Tom Moran may be reached at tmoran@starledger.com or call (973) 836-4909. Follow him on Twitter @tomamoran. Find NJ.com Opinion on Facebook.