My guess is that they would not mess with the 2nd Amendment following a WMD attack, but would simply curtail citizen movement temporarily.
After all, Myrddin, what would you suggest we do if underground terrorists snuck in a few nuclear bombs into the US and started setting them off at random.
My guess is that people would be demanding the military do something, and quick, to stop the massive carnage.
Furthermore, Tommy Franks is not a bone head simply for postulating what he thinks might happen were the US to be attacked by WMD.
What if alQadia successfully spread SMALLPOX around the country, and/or began spreading anthrax through the mail, or in subways.
Would the population get mad if some quasi military units clamped down temporarily.
Sure it would be scary, but I don't think we would have much choice.