The abrupt policy decision to seemingly abandon our Kurdish partners could not come at a worse time. The decision was made without consulting U.S. allies or senior U.S. military leadership and threatens to affect future partnerships at precisely the time we need them most, given the war-weariness of the American public coupled with ever more sophisticated enemies determined to come after us.

In northeastern Syria, we had one of the most successful partnerships. The Islamic State was using Syria as a sanctuary to support its operations in Iraq and globally, including by hosting and training foreign fighters. We had to go after ISIS quickly and effectively. The answer came in the form of a small band of Kurdish forces pinned up against the Turkish border and fighting for their lives against ISIS militants in the Syrian town of Kobane in 2014.

We had tried many other options first. The U.S. initially worked to partner with moderate Syrian rebel groups, investing $500 million in a train-and-equip program to build their capabilities to fight against ISIS in Syria. That endeavor failed, save for a small force in southeastern Syria near the American al-Tanf base, which began as a U.S. outpost to fight ISIS and remains today as a deterrent against Iran. So we turned to Turkey to identify alternative groups, but the Pentagon found that the force Turkey had trained was simply inadequate and would require tens of thousands of U.S. troops to bolster it in battle. With no public appetite for a full-scale U.S. ground invasion, we were forced to look elsewhere.

I (Joseph Votel) first met General Mazloum Abdi at a base in northern Syria in May 2016. From the start, it was obvious he was not only an impressive and thoughtful man, but a fighter who was clearly thinking about the strategic aspects of the campaign against ISIS and aware of the challenges of fighting a formidable enemy. He could see the long-term perils from the civil war, but recognized that the most immediate threat to his people was ISIS. After a fitful start in Syria, I concluded that we had finally found the right partner who could help us defeat ISIS without getting drawn into the murkier conflict against Bashar al-Assad’s regime.

The Syrian Democratic Forces (SDF), initially composed of the Kurdish People’s Protection Units (YPG), was then conceived: a fighting force that eventually grew to 60,000 battle-hardened and determined soldiers. The decision to partner with the YPG, beginning with the fight in Kobane, was made across two administrations and had required years of deliberation and planning, especially given the concerns of our NATO ally Turkey, who regards the SDF as an offshoot of the designated terrorist group the Kurdistan Workers’ Party (PKK). Eventually, the YPG became the backbone of the fighting force against ISIS in Syria. Without it, President Donald Trump could not have declared the complete defeat of ISIS.

With support from what grew to be the 80-member Coalition to Defeat ISIS, which included air power, advisers on the ground, and equipment, the SDF became a force to be reckoned with and led a string of victories. In August 2016, it liberated the Syrian town of Manbij, which once functioned as a hub for ISIS fighters to cross into Turkey and is believed to be where the attackers who carried out the November 2015 Paris attacks transited. Mindful of the need for credibility as it pushed to liberate Arab-dominated areas, the YPG had succeeded in incorporating Arab units into its structure as a united Arab-Kurd fighting force. That force, the SDF, went on to liberate the so-called capital of the caliphate, Raqqa, and towns in the Middle Euphrates River Valley, culminating in the territorial defeat of ISIS in Baghouz this past March.

Over four years, the SDF freed tens of thousands of square miles and millions of people from the grip of ISIS. Throughout the fight, it sustained nearly 11,000 casualties. By comparison, six U.S. service members, as well as two civilians, have been killed in the anti-ISIS campaign. Key to this effective relationship was mutual trust, constant communication, and clear expectations. The partnership was not without its difficulties. That included working through the December 2018 announcement of our sudden departure and our subsequent agreement with Turkey to pursue a security mechanism for the border areas. But each time, the strong mutual trust built on the ground between our military members and the SDF preserved our momentum. The sudden policy change this week breaks that trust at the most crucial juncture and leaves our partners with very limited options.

It didn’t have to be this way. The U.S. worked endlessly to placate our Turkish allies.

We engaged in countless rounds of negotiations, committing to establishing a security mechanism that included joint patrols in areas of concern to the Turks, and deploying 150 additional U.S. troops to help monitor and enforce the “safe zone.” Yet Ankara repeatedly reneged on its agreements with the U.S., deeming them inadequate and threatening to invade SDF-held areas, despite the presence of U.S. soldiers.

A possible invasion from Turkey against the Kurdish elements of the SDF, coupled with a hasty U.S. departure, now threaten to rapidly destabilize an already fragile security situation in Syria’s northeast, where ISIS’s physical caliphate was only recently defeated. Nearly 2,000 foreign fighters, about 9,000 Iraqi and Syrian fighters, and tens of thousands of ISIS family members are being held in detention facilities and displaced-persons camps in areas under SDF control. What happens if we leave? The SDF has already stated that it will have to fortify defense mechanisms along the Syrian-Turkish border, leaving ISIS detention facilities and encampments with little to no security. This is particularly troubling given the self-proclaimed caliph of ISIS Abu Bakr al-Baghdadi’s recent sermon called on supporters to break fighters out of these facilities, and amid violent attacks in the al-Hol refugee camp, where tens of thousands of women and children are housed and where ISIS sympathy runs rampant.

The Pentagon and White House later clarified that the U.S. was not abandoning the Kurds and did not support a Turkish incursion into Syria. But the damage may already be done, because it appears the Turks have taken the shift to signal a green light for an attack in the northeast. This policy abandonment threatens to undo five years’ worth of fighting against ISIS and will severely damage American credibility and reliability in any future fights where we need strong allies.