But in its most recent quarterly annual report on U.S. operations in Syria, released in August, the Defense Department’s inspector general said that “ISIS remains a threat in Iraq and Syria.” Former Defense Secretary James Mattis has also warned that the president’s decision to pull troops from Syria’s border in advance of a Turkish incursion could lead to ISIS’s resurgence.

Now, military officials on the ground say it’s already happening. ISIS has moved into a valley in a remote mountainous region in Northern Iraq. The valley is controlled by the Kurdish peshmerga on one side and the Iraqi army on the other. But along the dividing line between the two, there are areas — some as wide as five miles — where neither side patrols, giving the militants space to move.

And they do, coming out mainly at night.

“They have some tunnels, they have some caves,” said Gen. Sirwan Barzani, the commander of the Kurdish peshmerga forces, at a remote outpost atop a mountain in Makhmour that overlooks the valley. “And they are moving — especially at night.”