Among the United States' allies in the Middle East, few are as important — or as fickle — as Turkey. Lately, the diplomatic discord between them has been worse than usual. In an effort to ease the tension, Turkish Prime Minister Binali Yildirim traveled to Washington on Nov. 7, kicking off a four-day trip designed to settle a wide array of issues. But despite his best efforts, there are few clear ways to resolve the enduring differences between the countries or to address the new and complicated troubles that lie ahead. Bound by Ambition Turkey's stability is crucial to the United States' own success in the Middle East. Not only is Turkey an economic and diplomatic powerhouse in the region, but it also brings considerable military might to bear against the Islamic State .