I've actually always been perplexed on the bioterrorism - chemical terrorism - power grid attack issues. To my mind, they are the top "panic" alternatives.
Occam's Razor would suggest that the terrorists are just to dumb to do it. On the other hand, none of them are that tough to carry out. Perhaps so on a large and networked scale, but blowing up a critical substation that affects multiple cities, or a chemical release in a part of a city, or just letting a few people come into the country and be captured either carrying, or infected with, weaponized biologics would be enough to cause panic (with media assistance).
