First of all, the withdrawal process in Syria and Afghanistan will happen much more slowly than Trump initially claimed. Shortly after his shock announcement, the president offered significant caveats. On December 23, he tweeted that he and Turkish President Recep Tayyip Erdoğan had discussed “the slow & highly coordinated pullout of U.S. troops from the area.” On Sunday, Trump told reporters, “I never said we’re doing it that quickly.”

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The administration has added conditions for a departure from Syria that include defeating the last ISIS holdouts—“We won’t be finally pulled out until ISIS is gone,” Trump said—and protecting U.S. allies such as the Syrian Kurds. The U.S. National-Security Adviser John Bolton claimed that “the timetable flows from the policy decisions that we need to implement.” If the administration applies these benchmarks strictly, then even the beginning of the end in Syria recedes into the Levant horizon. ISIS, or its successor groups, will never be “gone.” ISIS militants can always abandon the physical caliphate and go underground, rebranding themselves as insurgents or terrorists. As for the Syrian Kurds, they will require protection indefinitely. They are threatened by two powerful enemies: Turkey, which considers Kurdish forces to essentially be terrorists, and Bashar al-Assad’s regime. If the conditions for a U.S. exit extend to checking Iranian influence in Syria or defending Israel, then withdrawal becomes even more fanciful. Tehran saved Assad’s regime at a cost of billions of dollars and is not about to leave.

On Monday, Trump claimed that he and his advisers were singing from the same hymnbook. “No different from my original statements, we will be leaving at a proper pace while at the same time continuing to fight ISIS and doing all else that is prudent and necessary!” he tweeted. Of course, taking prudent and necessary steps means slowing the pace of leaving.

Even if Trump fudges these benchmarks, or abandons them entirely, it’s exceedingly difficult to physically bring troops home. The process of leaving is known as “retrograde,” and is a logistical nightmare. The military has to box up and ship out a “Little America” of bases, Humvees, air conditioners, and even fast-food joints. Every gun and every bullet needs to be packed away, given to allies, or destroyed, to make sure they don’t fall into enemy hands. Removing one brigade of 2,000 to 5,000 soldiers from a combat zone can take weeks or months. A larger footprint can mean months or years. In Syria and Afghanistan, U.S. forces have to leave through forbidding terrain in an active war zone, without a nearby port.

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The kicker is that even if American troops do come home in a reasonably timely fashion, they will likely return before long. Recent U.S. campaigns in the Middle East have operated like a revolving door. In a globalized world, what happens in the Middle East affects U.S. interests and values. Recent presidents were all loathe to engage in prolonged conflicts in the region, but they were even less willing to—as they saw it—risk American security or lose a war.