Iran and Turkey are hardly natural allies. Iran is Shiite; Turkey is Sunni. Their predecessors, the Ottoman and Persian Empires, were neighbors who fought countless border wars (the boundaries of the current state of Iraq were a result). Finally, Iran was determined to keep Assad in power in Syria, while the Turks wanted to see the back of him. Historically, there isn’t much reason for cooperation there.
Until now. Today, they share the same large and deadly adversary–America. In addition to providing each other with diplomatic support, the Turks can and will help the Iranians bust the new sanctions. The two of them can also collaborate to make the lives of the Kurds and their American friends miserable in Syria. It’s going to happen, and we need to prepare for it.
The Turks have been difficult friends even under much better circumstances. Much of the blame for the current circumstances falls on them. Trump is making things worse, however, with his blundering, swaggering “diplomacy,” and we are going to pay a price for it in the near future.