Thats kinda wrong. Nukes have a hard time near the vacuum of space. There is simply not enough material to keep fission to create a good effect. In short his theory is wrong and convoluted and defies simple scientific facts regarding fission in space. EMP might be a problem but that in itself is theory. EMP could also just dissipate and have zero effect. Read below.
http://en.wikipedia.org/wiki/High-al...lear_explosion
But then the idea of a Nuke coming into American air space without detection and removal is pretty remote, its just not that easy to pull off.
In short I would not count on this happening anytime soon. Great read I am sure for paranoid folks there is a big market for it and giving another thing to be afraid of is big bucks!