Or one good suborbital thermonuclear blast
Frankly, it is no longer necessary to hit a city with a nuke. Or hit a target with a nuke.
Blowing a few 100 Kt up at ~ 80 miles up is enough to knock out the grid in a 500miles+ radius. There is no defense against this either - it is outside the short range interceptor range and it can pretend to be a satellite as far as anyone else is concerned all the way until it needs to execute Boom().