When Assad was just massacring people who wanted a less authoritarian government (I never felt they were going to build a real, functioning democracy but they have the right to try to anyway), I think it would have been helpful. Support for Assad was nebulous because the Iranians hadn't really thought long about whether or not they would lose their link to Hezbollah.

Back then, a bombing campaign would have worked. With the West's failure to act, however, the rebels have been taken over by al-Nusra and the new group, Jabhat Tahrir, as well as other smaller Salafist groups. Of the groups, Jabhat Tahrir seems to be the least threatening, at least for the present time, but its links with the Muslim Brotherhood in Egypt and its intolerance to non-Sunnis are problematic for any long-term solution in Syria.

Obama, as usual, is great at making speeches and nothing else. The single positive achievement of his Presidency, the killing of bin Laden, was urged by Clinton and Gates, and it was only after cancelling the operation once that Obama finally consented to it. I suspect that if the current foreign policy team had been in place then, we never would have done it because of the diplomatic consequences with Pakistan. Obama is even walking back his more or less effective drone strategy in the face of Leftist opposition.

Having said all of that, the US reputation is now on the line, for better or worse. The best option at this point is to go in heavy - drop more ordnance on Syria than was used since World War II, and do it with as much force as possible in the first 48 hours. Destroy all power for the capital, all television outlets, all palaces, carpet bomb front lines for the Assad forces, drop fuel-air bombs on every military base and about ten daisy cutters onto the Damascus airport and the port at Latakia (we would still have to avoid the Russian base, though, if we didn't want a diplomatic incident). Make sure that after a week, the Assad-controlled areas are devastated, and then let the rebels fight for control after that.

It would be the only way to send a message to the Iranians that we mean business.