Here's some perspective on just how massive Katrina was:
This is taken from the Katrina Information Map -- it's pretty cool. (Don't abuse it by adding garbage notes of course! There seem to be too many on it already.)
Now here's the same map with the effects of a small fission nuke (Hiroshima sized) superimposed in red:
When you consider how much infrastructure was taken out fairly far inland and the extent of power outages in the immediate aftermath, and then pile on the flooding of NOLA you get something that in many respects humbles the Apocalyptic effects of a small nuke.
In fact, the only small nuke hit that would even rival this would be one in NOLA that would (of course) have flooded the city. At least then folks would have realized not to pump the water out into the lake since it would be radioactive. (This idea of pumping the NOLA witch's flood brew out into the lake is going to end very badly I think; but that's a topic for another post.)
But for most cities that would be nuked, you just have to think about a nanosecond to realize that while the death toll would be hugely higher given the likelihood of no warning at all (it's now looking like the low thousands at worst), it would actually be a lot easier to get help to the survivors on the fringes since the damage would extend only to approximately the outer red ring rather than the huge rounded rectangle of the Katrina map. In general, you could get there from wherever the supplies were since the infrastructure damage would be much more localized.
Aside from the whole issue of Federalism and whether W should have invoked the Insurrection Act -- and perhaps also aside from the general pychological effects of nuclear weapons -- it would be easier to get aid to the survivors of a nuke than those from Katrina.
Tinfoil Apocalypse? Yes, the Apocalypse is coming folks. But not in the fantasmagorical imagery of Revelations. In the form of insane, nihilistic Islamic lunatics wearing "Tinfoil Hats" finally getting their fingers on the "red button" and treating it like a door knocker.
It might take Iran a number of years to develop them themselves. Or maybe OBL has already acquired them from the NorKorComs or the Russian Mafia.
Who knows? Certainly not the CIA, that's for certain.
But too much technology in the hands of the too very intensely insane can only end badly.
Very badly.
But, surprisingly, in many ways possibly not as badly as Katrina...