Preserving the Syrian Democratic Forces is key to preventing an Islamic State resurgence after the withdrawal of U.S. troops from Syria, according to the former special envoy to the counter-ISIS coalition.

But Brett McGurk, who resigned from his State Department post in December, says the U.S. is increasingly losing its grasp on keeping the Kurdish-led SDF together.

“I think the ability of the United States to hold the SDF intact, which is critical to mitigating the risk of an ISIS resurgence, is draining by the day,” McGurk said at an event Monday hosted by the Foundation for Defense of Democracies.

“I think the threats at this stage, there’s a very high risk that they’ll reemerge,” McGurk said.

The SDF is composed of Syrian Kurds, Arabs, and other ethnic groups.

McGurk, who President Barack Obama appointed as the special envoy to the counter-ISIS coalition in 2015, resigned in December 2018 after President Donald Trump announced that ISIS had been defeated and that all troops would return home. The announcement sparked backlash and also was a factor in former Secretary of Defense Jim Mattis’ resignation last year.

Although not all troops were withdrawn following Trump’s December announcement, he announced earlier this month that U.S. troops would be pulled from northern Syria.

The decision essentially paved the way for Turkey to launch an operation in the region against the Kurds, who have fought alongside the U.S. to combat the Islamic State. However, Turkey views Kurds with the Syrian Democratic Forces as a branch of a designated terrorist organization.

“I’ve seen this movie before. It’s like the second version of the movie, it’s worse than the first,” McGurk said. “We’re now going to keep a small presence somewhere, but we’ve already abandoned most of our positions — we’re giving them to the Russians, we’re bombing them as we leave.”

Two U.S. F-15E fighter jets conducted airstrikes on Wednesday to wipe out ammunition remaining from U.S. troops exiting Syria. U.S. Army Col. Myles Caggins, a spokesman for Operation Inherent Resolve, said the strikes were pre-planned.

Meanwhile, a video was posted to Twitter last week depicting Russian forces taking over bases that reportedly used to be a U.S. camp.

The withdrawal has sparked outrage among local residents as well. Earlier Monday, reports emerged that a U.S. military convoy was assaulted with tomatoes as it was departing Syria. The online Kurdish media outlet, Hawar News Agency, posted video of the incident.

But McGurk said it wasn’t always this way. In fact, U.S. troops had significant support in Syria and service members who were stationed in Syria claimed it was the most “permissive post-war environment” they had experienced, he said.

“Thousands of people all supported our presence,” McGurk said. “That’s why we’re able to work in that environment, keep a light footprint. And now we’re leaving and tomatoes are being thrown at our vehicles with an American flag on it.”

“I think it is shameful, I think it’s going to get worse,” McGurk said.

Secretary of Defense Mark Esper told reporters on his way to Afghanistan this weekend that U.S. troops from Syria would head to Iraq to conduct counter-terrorism operations, but Esper said Monday that the Pentagon is weighing keeping some U.S. troops in Syria to safeguard oil from ISIS.