“A country is going to start a nuclear war with us just to shutdown some of our electronics?”
If I (with no military or intelligence experience whatsoever) can think of the following scenario, then trained and experienced people in nations hostile to us can certainly do better: Put one of your nukes on an unmarked and/or unregistered barge or other very expendable small ship, sail it to a couple hundred miles off of the U.S. coast, launch the missile to detonate the nuke at about 50 miles above the surface, sink the boat (in 10,000 or more feet of water), and get out of the area as fast as possible. Do this off of the East Coast, West Coast and Gulf Coast - now you’ve hit all three electrical grids that we have.
That’s not too hard or imaginative, but it makes tracing the owner of said missile and nuke much more difficult. A nation intent upon totally screwing up power generation (and thus production and delivery of fuel, fertilizer, medicines, running water, etc., etc., etc.) could do so with a very reduced expectation of facing our wrath.
Highly unlikely that anyone other than a few declared nuclear powers could launch something off a ship that would be more than a nuisance (and suicide note for he attacker), and if they did there is no way it isn’t traced by satellite recon and other measures currently present on the coasts.
Lastly, there are not 3 grids-—there are 4. Texas has it’s own.