U.S. and Turkish efforts to ramp up military action against Islamic State and to create “safe zones”—or, at least, ISIS-free areas—in northern Syria renews attention on U.S. policy toward Syria. Should the Obama administration concentrate on hitting ISIS or take on the challenge of trying to weaken and ultimately remove Syrian President Bashar al-Assad by force or diplomacy? Getting rid of the Assad regime is critical for a stable Syria. But that’s unlikely to be the administration’s immediate priority for several reasons.

Tehran won’t bite now: To have any chance of easing or forcing Mr. Assad from power, the U.S. will need Iranian buy-in. And right now there’s just no way Washington will get it.