This is what I'm getting at. If the US wanted to remove Assad, he wouldn't have much of a choice: a life of luxury in exile, or death. I disagree, however, that it would require tanks. They could do the same as they did in Libya, which is far more justifiable and politically expedient. The dissidents in Syria are gearing up for war[1], so the ever-problematic boots on the ground would be unnecessary.
The US would only have to make Assad think it was serious about another Libya in order to give him some serious misgivings. Get NATO to make some rumblings, which would encourage Chavez to issue one of his proclamations against American Imperialism, then make a backroom deal to get Assad out.
At the end of the day, the Bush Doctrine of democracy-at-swordpoint is simply ineffective. There exists, however, the very real possibility of using soft/"firm" power to encourage the outcomes you want.