Thehill.com | By Eric R. Mandel, Opinion Contributor

In 2019, against the advice of many foreign policy and defense officials, President Trump abandoned our Syrian Kurdish allies, who were front-line in helping us eradicate the ISIS caliphate. Trump acquiesced to Turkish President Recep Tayyip Erdoğan’s invasion, which caused an estimated 300,000 Kurds to become refugees. The Kurdish forces lost 11,000 fighters in the war against ISIS, and their abandonment sent a chilling message to American allies worldwide. 

At the time, Joe Biden said, “Donald Trump sold out the Syrian Democratic Forces — the courageous Kurds and Arabs who fought with us to smash ISIS’s caliphate — and he betrayed a key local ally in the fight against terrorism.” 

Fast forward to 2022 and another Turkish invasion is on the horizon that could overwhelm Kurdish forces, who now incarcerate more than 10,000 ISIS prisoners. The ISIS terrorists are just waiting for an opportunity to escape and restart their jihad. In January, there was a significant prison break at the Ghwayran prison in Hassakeh.  

Preventing the resurgence of ISIS is still an American priority and a prime reason we have 900 U.S. troops aiding the Kurdish forces. Our small footprint has given us disproportionate security influence, which could disappear in the blink of an eye with a full-scale Turkish invasion. Unfortunately, our NATO ally Turkey’s priority appears to be not ISIS but eliminating the Kurds.

The Syrian Democratic Forces (SDF), whose primary contingency is the Kurdish YPG, has said that to defend the Kurdish region from a massive ground attack, they will focus their forces against the invasion. That means soldiers guarding the ISIS prisoners could leave overnight. SDF Commander Mazloum Abdi told The Associated Press, “If Turkey attacks … the war will spread to all regions. … We can say that our work against IS with the international coalition has stopped because we are preoccupied with the Turkish attacks.” 

According to Fox News’s Jennifer Griffith, “There is significant concern that Turkey’s planned ground invasion into Syria … could open the floodgates for the release of thousands of imprisoned Islamic State terrorists … from more than 50 countries.”  

Turkey is preparing for its fifth and possibly ultimate ground war in northern and eastern Syria. Turkey considers the Syria Kurdish forces to be an arm of the Turkish Kurdish PKK, a U.S.-listed terrorist group. The United States disagrees. Turkey’s goal is to create a permanent 20-mile-deep security zone in Syria along the Turkish border. The territory, once emptied of Kurds, would be used to resettle Syrian refugees living in Turkey who were displaced during the Syrian civil war. However, Article 49 of the Fourth Geneva Convention prohibits the deportation of a civilian population.  

With Russia’s war in Ukraine and protests in Iran ongoing, President Biden may believe that the U.S. is too overextended to deal with an invasion by Turkey. That would be a mistake, as a resurgent ISIS would call the U.S. back to a far more chaotic Middle East.

In 2019, Biden said Trump sold out the Kurds and forced them to “defend themselves against Turkey instead of fighting ISIS.” The president can show true leadership and back up his words by using his leverage to pressure Erdoğan to stop his invasion. At the G-20 summit, Biden expressed condolences to Erdoğan for this month’s terrorist attack in Istanbul and told him that “we stand with our NATO ally.” But there was no warning against a ground invasion in the White House readout. That’s not a good sign.  

Erdoğan has made a calculated decision that the Biden administration, like the Trump administration, will not impose any significant consequences in response to an invasion, and that he can act with impunity because NATO needs his approval to allow Finland and Sweden to join the alliance.

But with Turkey’s economy in turmoil, and his party losing in the polls, an invasion of Syria’s Kurdish region may be more about domestic politics and influencing the upcoming Turkish election. By appealing to the Turkish people’s nationalism, Erdoğan may be hoping to change the focus from their economic woes toward a common external enemy and bring him another electoral victory.

Biden may not have enough leverage or options to dissuade Erdoğan. But he needs to let him know that if Turkey chooses not to play ball, there will be real consequences. The president should speak with Erdoğan and convince him to put his offensive on hold indefinitely — or the U.S. will hold him responsible for the resurrection of ISIS and another humanitarian refugee disaster. Unfortunately, the Biden team appears resigned to sacrificing the Kurds to Erdoğan’s ambition.

A Turkish invasion also would be a victory for Russia. Turkey, Russia and Iran are part of the Astana agreement, a plan to divvy up Syria. According to Soner Cagaptay of the Washington Institute, Russia may be “angling for a deal between Ankara and Damascus that could wrap up the war in Syria,” leaving Iran, Russia and Turkey with their share of the Syrian pie.  

Many Americans may have forgotten about the Islamic State and its threats against the West. But if the terrorists rise again, with images of rape, plunder and beheadings resulting from the Turkish invasion, the American public might not be so forgiving of Biden for being blindsided by this. We devastated ISIS once, at an enormous cost. We don’t want to have to do it again.

Dr. Eric R. Mandel is the director of MEPIN, the Middle East Political Information Network. He regularly briefs members of Congress and their foreign policy aides. He is the senior security editor for the Jerusalem Report. Follow him on Twitter @MepinOrg.