we aren't going to nuke a city like Mecca UNLESS the attack came from there.
I know someone will say "well they're islamic so it came from there" but no one will see it that way so it's unrealistic to say so.
Damascus isn't stupid enough to go through with anything like that unless they think they can win.
But they probably ALSO know that anything that gets traced back to them means instant regime change. They aren't THAT stupid, only Saddam was.
We won't go strategic nuke unless someone big (Iran) hits us. If it's AQ, we will use "smaller" nukes.
The fact that we are even discussing nukes should dissuade them unless they are as stupid as they make themselves out to be.