Turkey's offensive in Syria leaves U.S. in a bind

Military vehicles in Turkey this month. Photo: Hilmi Tunahan Karakaya / Anadolu Agency / Getty Images

Trump's homeland security advisor Tom Bossert said the U.S. would prefer Turkey exit from Afrin, Syria, where it's been launching an assault on U.S.-backed Kurdish forces. That's a shift from just earlier this week when U.S. Secretary of State Rex Tillerson said he hoped Turkey would exercise "restraint" in the offensive.

What's happening: Turkey's entrance for the first time as an overt combatant in the war is dramatically shifting the political calculus of the war, and exposing a new challenge for the Trump administration: delineating the boundaries, physical and otherwise, of U.S. involvement in Syria post-ISIS.