Turkey is a US ally and a NATO member, but under President Erdogan’s assertive foreign policy, Ankara has shown the capacity to go its own way if necessary. American and Turkish leaders, Joe Biden and Recep Tayyip Erdogan, will meet on June 14 at the NATO summit amid a backdrop of serious disagreements on various issues, ranging from Ankara’s purchase of Russian S-400s to Washington’s ongoing support of the YPG ...