To some extent I can believe it -- they believe their own propoganda...and they're not the first to fall into that trap.
They also see how long and hard the diplomatic manuever regarding Iraq took, on top of the 12 years before that. Assad may just think that "we wouldn't dare" go after him on the fly, making France/Germany/Russia just that much more upset.
Assad is nutty enough to believe both things and not be paying attention to the very powerful "follow on" forces we have just entering the theatre. If he gave us a really good reason (like acquiring some of Iraq's WMD's (mobile bio labs or such) or actually started to foment serious terrorist disruption in Iraq, then it wouldn't be all that difficult to take him out. We've probably got Special Ops over his border right now anyway. But Israel would be attacked this time, so the situation could get interesting.