A new book on threats to the USA has been published. Article here. Of interest (to me anyway) is the mention of an electro magnetic pulse attack (EMP) on the USA by means of a sub-orbital nuclear weapon. The idea is that a foreign power such as N.Korea, Chicom China or what have you would launch a ballistic missile over the continental USA and fry all the computers, telephones and power transmission facilities with an EMP from a nuke.
Technically this is within the grasp of Al Qaeda and the various nut regimes of the world. It would damage the USA considerably and cost them astounding ammounts of money as well, and as the author says it would take years for them to come back from such an attack. Its the kind of thing Cold War USSR planners would think of, because they had the hordes of tanks and giant armies to come in behind such an attack and make use of the opening.
These days though we face people like Ossama and Kim Jong Ill who think terror is where its at. Their goal is to terrify and cow the American populace. They wanna scare Joe Sixpack.
Knocking out phones, lights and computers is not going to scare Joe Sixpack. It might kill him, expecially in winter, but it won't scare him. Nuking a city is scary. Shutting off the power is dangerous, but mostly its annoying.
Such an attack would instantly unify and harden the civilians of the USA into a WWII-style culture. That is the absolute worst case scenario for a smaller opponent. Therefore it is most unlikely. Knock wood of course, one never knows how stupid one's opponents are.