But one over the North East is enough to send the USA into a tail spin.
There was an old saying back in the '80's: There are 3 superpowers, the Soviet Union, the United States and a Trident Submarine. The "boomer" submarines are normally real deep and unaffected by such attacks, at any given time. Enough nuc-power to neutralize any country.
The key is trucks, tractor trailers. If they can keep running in various areas, we can rebuild fast. If you have not read that book, than you will enjoy it I am sure.
The trucks would likely be toast. The other thing that would be toast are large electrical smelters. You need them to make the iron cores for the transformers.
The good news is you can make them in Korea and ship them here if the US is on its back.
I’ll look into the book.
If you really want a feel for how vulnerable we are through IT, you can spend a few hours at the link:
http://conference.hitb.org/hitbsecconf2013ams/materials/
Have fun.