It would need a hydrogen bomb and a very powerful booster, and it would not cripple the U.S. ability to respond, since most of the U.S. military force would be under the sea or over the horizon from the EMP.
But the issue is “respond against whom?” Ultimately we might be able to discover who sent the nuke but that could take lots of time and you would want to be damned sure you had the right people identified.
But would Obama have the guts to pull the nuke trigger on fellow muslims?
1 EMP bomb would send a lot of people back to the stone age. And nobody would have a idea what the hell happened.
“It would need a hydrogen bomb and a very powerful booster”
Actually a fission only device with thin case construction will supposedly generate a more powerful EMP than most much larger megaton thermonuclear devices.
http://en.wikipedia.org/wiki/Electromagnetic_pulse