During the war against ISIS, the U.S. was able to quell Turkey's concerns [about U.S. cooperation with the YPG] with the greater good. Kick the can down the road, if you will. [With the counter-ISIS fight winding down,] Turkey sees [continued U.S.] partnership [with the YPG] as an American security guarantee for the YPG and their activities in the region. The U.S., on the other hand, sees its presence as vital to counter Iranian influence and to support the liberated areas. What's happened in Afrin is bringing the contradictions of U.S. policy to the forefront. The move to build a border security force has led Turkey to further doubt the U.S... The U.S. needs a coherent internal plan to solve their differences, and then come up with a regional plan for Syria.