Withdrawing U.S. troops from northern Syria jeopardizes American credibility among allies and could unravel progress already made to quash the Islamic State, according to retired Gen. Joseph Votel.

“The abrupt policy decision to seemingly abandon our Kurdish partners could not come at a worse time,” Votel and Elizabeth Dent, a non-resident scholar with the Middle East Institute’s Countering Terrorism and Extremism program and former State Department official, wrote in an op-ed for The Atlantic Tuesday.

“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,” they wrote.

On Sunday, the White House decided to withdraw U.S. troops from the Syrian-Turkish border amid an impending attack from Turkey against Syrian Kurds. Although Kurdish allies have fought alongside U.S. forces to combat ISIS, Turkey considers Kurds with the Syrian Democratic Forces a branch of a designated terrorist organization.

The move has ignited outrage from lawmakers on both sides of the aisle, but President Donald Trump has defended the policy shift. A senior administration official also told reporters Monday that the move was not a complete withdrawal of U.S. troops in Syria. Rather, the decision would move between 50 to 100 U.S. special operations forces to other locations in Syria.

Votel and Dent argued that one of the most “successful partnerships” was born in northeastern Syria between the U.S. and the Syrian Democratic Forces, which evolved from the Kurdish People’s Protection Units into a force of 60,000 soldiers.

“Eventually, the YPG became the backbone of the fighting force against ISIS in Syria,” Votel and Dent wrote. “Without it, President Donald Trump could not have declared the complete defeat of ISIS.”

Votel and Dent cited multiple contributions from the Syrian Democratic Forces, including liberating the Syrian town of Manbij that ISIS fighters used to enter Turkey and liberating the Syrian town of Raqqa that ISIS claimed was the caliphate’s capital.

In order for the partnership to thrive, Votel and Dent said “mutual trust, constant communication, and clear expectations” were necessary.

“The sudden policy change this week breaks that trust at the most crucial juncture and leaves our partners with very limited options,” they wrote.

Votel and Dent also noted the Syrian Democratic Forces sustained nearly 11,000 casualties over the past four years combating ISIS. So far, the U.S. has suffered casualties of six service members and two civilians in the fight against ISIS in Syria.

U.S. efforts to “placate our Turkish allies” proved unsuccessful, according to Votel and Dent. They claimed Turkey “repeatedly reneged on agreements with the U.S.” following multiple rounds of negotiations regarding a security mechanism at the border.

An invasion from Turkey against Kurds with the Syrian Democratic Forces, “coupled with a hasty U.S. departure, now threaten to rapidly destabilize and already fragile security situation in Syria’s northeast.”

Although Votel and Dent claimed U.S. allies and senior U.S. military leadership were not consulted, the Pentagon has pushed back on “misreporting” and said that Secretary of Defense Mark Esper and Chairman of the Joint Chiefs of Staff Gen. Mark Milley were consulted.

“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,” Votel and Dent wrote. “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.”

Turkey announced early Wednesday that Turkish Armed Forces and the Syrian National Army was launching its operation in northeastern Syria. Later Wednesday, Syrian Democratic Forces spokesman Mustafa Bali tweeted “Turkish warplanes have started to carry out airstrikes on civilian areas.”

The Trump administration first announced in December 2018 that ISIS had been “defeated” and that U.S. troops stationed in Syria would return home. The announcement played a role in the resignation of former Secretary of Defense Jim Mattis.

Votel served as the commander of U.S. Central Command from March 2016 to March 2019.