Defense Secretary Mark Esper refused to put a timeline on the Pentagon’s scaled-down mission to defeat the Islamic State and guard Syrian oil fields at the agency’s last press briefing of the year.

Conditions-based: "That's a crystal ball that I don't have,” Esper responded when asked when 600 US troops in the war-torn country would leave. “I think we're there as long as we can ensure the enduring defeat of ISIS."

Why it matters: The Pentagon has long insisted that the US troop presence in Syria will be “conditions-based,” meaning that American forces will leave when the agency determines local military and police units can manage the terror fight on their own. Yet Esper’s inability to answer for the timeline possibly indicates that the plan to shift more forces away from the Middle East could face delays, even after President Donald Trump repeatedly called for a withdrawal.

Pivoting to Asia: "None of us want forever wars," Chairman of the Joint Chiefs of Staff Gen. Mark Milley chimed in. Esper says his overall goal is to eventually move more American troops in the Middle East to the Asia-Pacific, in line with the 2018 US defense strategy, despite the Trump administration adding 14,000 troops to the region since May to deal with an uptick in tensions with Iran.