Every metropolitan area would be on edge as never before. Would urban residents be evacuating in a panic upon news of another city being hit? Would you?
Having watched the city of Houston try to evacuate past my front door before hurricane Rita, I think I'd still just bug in even if a nuke went off downtown. Actually, a smart terrorist would set the nuke off in the middle of the refineries on the south side of town. That would be 70 miles from me.
I do suspect most other residents of Houston would be running out of the city in fear.
-Blast