James Mattis in New Yorker

On War & Peace: Keep U.S. troops in Syria indefinitely to defeat ISIS

By then, 95% of the ISIS pseudo-caliphate in Syria and Iraq--once the size of Indiana--had been liberated. No longer. ISIS is now making a comeback. Two stunning reports this month--by the United Nations and Trump's own Defense Department--both contradict earlier US claims that most ISIS fighters had been eliminated. The Pentagon report [says] ISIS has successfully morphed from a proto-state into a "covert global network, with a weakened yet enduring core" in Iraq and Syria.

So the Trump Administration has reversed course; it is now keeping U.S. troops in Syria indefinitely.

On War & Peace: Keep U.S. troops in Syria indefinitely to defeat ISIS

The US has three missions to complete before it can withdraw. "One, we have to destroy ISIS. The President's been very clear that ISIS is to be taken out," Secretary of Defense James Mattis said on August 28th. "We also have to have trained local troops who can take over."

The Trump Administration also does not want to withdraw U.S. troops, Mattis said, until a peace process is under way to end the war in Syria and map the country's political future. "We need the Geneva process--the UN-recognized process--to start making traction towards solving this war," Mattis said. "Now, if the locals are able to keep the security, obviously during this time we might be reducing our troops commensurate with their ability to deny ISIS a return, but it really comes down to finding a way to solve this problem of Assad's making."