All our serious enemies (Iran, NK, Chavez, Castro,...) understand that successfully delivering a high EMP yield weapon would be a knockout blow. We would be left with our submarines. They could destroy all our enemies. That should be made clear to the Russians and Chinese. They may be able to knock out our electric grid, but they will have nothing left but smoldering craters.
Say an EMP delivered FROM a site off the coast - or from a land missile in Nebraska ... get that baby up in the air 125 miles - and most of the US is taken out. How do we retaliate? Aim are stuff at who? Our planes have their chips fried - they're grounded - for good. Communication systems down - everywhere. Missile command structure inoperable... We'd have no clue who did it...
Our best people would be dealing with important things - like keeping their families from starving to death.
Our subs could knock out Russia or China - or Iran - or North Korea or some terrorist cell supported by a rich ME country... But we'd better guess well ...
'cause things can get worse.