If the threat of conventional attacks by terrorists aren't enough for you, consider the EMP scenario. Bad guys detonate a nuclear weapon high above US soil, triggering an electromagnetic pulse that knocks out all electronics and renders the US helpless. The conservative Heritage Foundation is so worried it's calling on Congress to get serious about preparing for such an attack. It even wants an EMP Recognition Day.
Skeptics include Mark Thompson at Time. "Leaving aside the contradiction of urging Congress to concentrate attention and resources on a threat that most in Washington consider an infinitesimal probability, the whole notion seems rooted in some visceral need for foes with diabolical destructive abilities. There's something almost pathetic about cowering in the shadow of such a threat, instead of shrugging it off with the resilience that was typical on the American frontier." (Read more nuclear attack stories.)