These partnerships have proved invaluable in the war against ISIS. At the same time, they have also opened a small hole in the secrecy that typically shrouds the Special Operations community—by giving the local partners who work with these forces a rare and up-close view of who they are and how they do their jobs.

In Syria, elite U.S. troops among the 1,000 American personnel in the country worked closely with Kurdish counterterrorism units while regular Kurdish fighters carried out most of the ground operations against ISIS. The U.S. partnership with the Kurds grew as America armed and trained them and later merged them with Arab groups under an umbrella militia called the Syrian Democratic Forces. The SDF spearheaded the fight against ISIS in Syria, rolling back its most important strongholds. It has said that it lost more than 10,000 soldiers in that fight.

Read: The forever war fought by America’s allies

U.S. military officials wasted no opportunity to laud the SDF’s prowess. So President Donald Trump’s announcement of a hasty and ill-planned withdrawal of U.S. troops from Syria to allow for a Turkish onslaught left everyone—allies, lawmakers, defense officials, but most significantly the Kurdish-led forces themselves—stunned. Fearing for its existence in the face of an invasion from NATO-allied Turkey, which considers it an enemy, the SDF has rushed to strike a deal with the Iran- and Russia-backed Bashar al-Assad regime. While the details of this arrangement remain in flux, one possibility is for SDF forces to be folded into the Syrian state, following negotiations to which they suddenly bring very little leverage. As a result, the same Kurdish counterterrorism units that have worked with U.S. Special Operations forces and intelligence may suddenly find themselves working with—or at the mercy of—the Syrian government. This raises a vexing counterintelligence question for America: Might these units be forced to spill their secrets to some of America’s foremost global adversaries, in Assad, Russia, and Iran?

Eric L. Robinson, a former U.S. intelligence official who worked on anti-ISIS strategy at the National Counterterrorism Center, calls the fact that the SDF was forced to seek Assad’s protection in Syria a counterintelligence “nightmare.” He worried, in a Twitter post this week, that “given years of SDF exposure” to U.S. Special Operations forces and intelligence, it would “be forced to give up TTPs [tactics, techniques, and procedures], names, locations, etc. What a coup for the Russian intelligence services—five years of history regarding the elite forces of NATO.”

Robinson, who was a senior civilian in the United States Special Operations Command until last year, also noted that the same elite troops who served in Syria also work around the world on America’s most sensitive national-security missions. They’re “from the same community that relieves an embassy under siege, identifies [North Korean] mobile missile capacity, rescues hostages, or defends Tallinn from [a] Russian invasion,” he wrote.