Turkey's Erdogan has again promised to invade Syria and establish a "safe zone" extending 20 miles into Syrian territory along 300 miles of Syria/Turkey border. What will happen to the US-backed Kurds, who Erdogan calls "terrorists," that live in that area? What about US military installations that may exist in the "safe zone"? For that matter, what will Putin and Rouhani have to say about Erdogan's threats?