Mention “Recep Tayyip Erdogan” to a U.S. national security official. Chances are, you will see a few eye rolls.

The Turkish president has made a name for himself as a brash nationalist who is more than willing to tug at Russian President Vladimir Putin’s sleeve for advanced weaponry despite his country’s membership in NATO. Turkey’s deployment of the Russian-manufactured S-400 missile defense system continues to hamper Ankara’s ties with Washington.