Will the US and Turkey break up over Russian S-400?

WASHINGTON, DC - Fans of diplomatic history realize the importance of dates: They mark milestones, turning points, make-or-break moments. Those who follow Turkey are keenly aware that a new era in the country's diplomatic history is taking shape before us. March 4 and 5, 2019 are sure to become important dates in this new diplomatic history.

This past Monday, reversing a trend of handling issues with Ankara quietly and in private, US President Donald Trump sent a letter to Congress calling for the termination of preferential trade treatment for Turkey. Most of Turkey's exports to the US have enjoyed duty-free treatment since 1975.

Then on Tuesday, General Curtis Scaparrotti, commander of US European Command and Supreme Allied Commander of NATO, responded to an inquiry from the Senate Armed Services Committee as to what he would advise if Turkey went ahead with its...