Enough is enough: the world must end Syrian nightmare
"The US may find it necessary to mobilise international support to launch strikes in Syria against both the regime and positions held by extremist groups. The strikes would in all likelihood need to be significant and sustained enough to change the calculations of the combatants."
I don't think this is the best idea, but I don't see how it means that an Iraq-style invasion would follow if the airstrikes didn't work. But I think the argument works the other way round, if support does not go to the actual rebels, the barbarity of a desperate régime and the vacuum filled by al-Qaida styley formations means that the pressure for some sort of intervention becomes unstoppable.