Heras stressed that it’s still unclear what will become of the YPG and its counterterrorism units under a deal with Assad, though he noted that integration into the Syrian security forces is one likely possibility. Even setting aside the potential counterintelligence risk that would come with the YPG switching sides, he added, the U.S. will suffer a major intelligence setback with the loss of a crucial partner.
“This kind of hasty withdrawal creates a collapse in our intelligence collection on ISIS,” Katz, the former CIA official, told me. “People sometimes think there’s this magical intelligence button that the military and intelligence community hits—boom, start collection now. But building an accurate and active intelligence picture of a terrorist group, and one as savvy and sophisticated as ISIS, is a tedious and years-long enterprise.”
All of that is now at risk of being lost. “It’s human intelligence that gives the U.S. government its best ability to understand the strategic plans and intentions of terrorist groups—not only their movements on the ground, but their plotting of extremist attacks,” Katz said. “And human intelligence requires proximity and access and trust and building relationships with sources on the ground.”
Another ramification for the U.S. intelligence community is the potential for mass escapes of ISIS prisoners. The SDF holds thousands of suspected ISIS militants, including many foreign fighters, in its territory. Some prison breaks have already been reported, and the fate of the prisoners who remain in SDF hands is uncertain. Heras, the Center for a New American Security expert, told me that the possibilities are grim: More could escape, or all could be handed over to the Assad regime, which could torture and execute them, or perhaps seek to co-opt them, as it did in sending jihadists against U.S. troops during the Iraq War.
Read: There is no Plan B for ISIS prisoners
Regardless, U.S. investigators will likely lose access to a vital source of information about ISIS. One former U.S. military officer who worked at senior levels of the anti-ISIS campaign told me he doubted that U.S. investigators had managed to interview all the ISIS prisoners, especially those captured more recently. “We’ll lose out on interrogations that didn’t happen and on follow-on interrogations that won’t happen,” he said, speaking on the condition of anonymity due to the sensitivity of the issue. “The historical knowledge that’s resident there would take years to get through. And that’s knowledge that we’re probably not going to have access to.”
Anne Speckhard, who directs the International Center for the Study of Violent Extremism, has interviewed dozens of the suspected ISIS prisoners held in SDF prisons. She told me that many had turned against ISIS and were powerful voices in persuading others not to join militant groups. “Most of the people that we interviewed got disillusioned by ISIS—and got disillusioned because they felt ISIS is un-Islamic, corrupt, and really brutal,” she said. “We’re just losing a gold mine of data.”