The “moderate” Syrian opposition are taking the same position as Turkey in demanding that the U.S. attack the Assad regime before they support the war on ISIS:

The rebels say they have been put in a difficult position in which they are being asked to support a strategy that has so far brought them no benefits and is regarded with suspicion by ordinary Syrians. They are now insisting they will not support the strikes unless the strategy is extended to include toppling the Assad regime — a position shared by Turkey, which hosts the rebel leadership.

The rebels’ position is entirely understandable, but it is also another argument for bringing the intervention to an end. It is unreasonable to expect anti-regime forces to do Washington’s bidding against other enemies of the regime when their overriding concern is to fight regime forces. However, that isn’t an argument for doing what the rebels want. It draws our attention back to why the war has been misguided and unlikely to succeed from the start, especially once it expanded into Syria. If both Turkey and the “moderate” opposition refuse to cooperate unless the U.S. attacks the Syrian government, that tells us that the war against ISIS cannot be fought effectively at an acceptable cost. That should be a clear warning to the administration to stop now before it gets in any deeper. Warring against both sides in the same civil war not only appears absurd, but it greatly increases the chances of costly failure.

Commencing hostilities with the Syrian government now not only puts American pilots at greater risk as they carry out attacks on ISIS, but it could also have other dangerous consequences for U.S. relations with Russia and Iran. Suppose that U.S. strikes on regime forces kill Russian or Iranian advisers. At best, that will seriously harm relations, and it could spark a new crisis or perhaps even some form of retaliation on the part of the Iranians and their proxies. Even if that doesn’t happen, we have to assume that attacking the Syrian government will strengthen the position of hard-liners in Iran to everyone’s detriment. If the administration caved in to these demands to attack the regime, it would be only a matter of time before the rebels issued new demands for a larger U.S. effort to oust Assad.