followed by

"RICE: INTELLIGENCE INDICATES IRAN BEHIND ATTACK"

followed by

"ANALYSIS CONFIRMS NUCLEAR MATERIAL STOLEN FROM U.S."

and so on.

It wouldn't matter that it was our own nuclear material used in the bomb, the administration could "discover" some "missing" material.  OMFG, those bastards stole it from x country that we gave some material to for supposedly peaceful purposes!  Or perhaps we have some Russian plutonium lying around, in which case, it would even be believable that the material was acquired on the black market.  

Some "thwarted plot" just wouldn't force most people to roll over and play dead..an actual attack probably would, although not likely quite as badly as after 9/11, I'm sure there would still be relative calm from the opposition...