Turkish leaders regard the Kurdish enclaves in both Syria and Iraq a serious threat to Turkey's own security and territorial integrity. That is not an irrational fear, since roughly half of the Kurdish population in the Middle East resides in Turkey, and the Marxist Kurdistan Workers Party (PKK) has waged an intermittent secessionist war against Ankara for more than three decades. Erdogan charges that the PKK is a terrorist organization and that Syrian Kurds have close ties to the PKK. He is not entirely wrong; the largest faction did begin as a PKK offshoot.
Unless Washington is willing to keep U.S. troops in Syria as buffer between Turkish and Kurdish forces indefinitely, there is no way to prevent a showdown. Opponents of Trump's initial withdrawal decision implicitly seem to be adopting [the independnet forces] position. But America already has one forever war in Afghanistan. Only the most masochistic individuals would wish to acquire another one in Syria.