Autz - I read your Op and I have an answer. No.
I do not think there will be a massive biological.nuclear attack on the United States. One of our biggest and most formidable defenses is the sheer size of our country, and the massive oceans seperating us from the rest of the world.
Looking at your OP you are in Tucson. I would not worry about much there, Autz ok. I seriously doubt any terrorist is going to blow up Palo Verde Nuke plant, especially with all those jets flying around from Luke.
I think you need to do some more research, and really take a good look at what is actually happening in the world. Understanding can be a very good friend.
There are certainly people in the world that want to do the US harm, on a grand scale. But I certainly believe they do not have the means to carry out the kind of large scale attack you are postulating. A small attack possibly, maybe even a series of small devistating attacks. But not mass murder or a nuclear bomb, I just do not see it happening…