Let’s say the EMP warheads were launched from Submarines off the east and west coasts in international waters. No country has any defense for that, going further, what if the EMP effects were only along the east and west coasts maybe 100 miles inland, it would be devastating and yes, we could respond with a nuclear response, then what at that point it’s Armageddon.
Russia and China likely not going to risk the response, what about Iran or North Korea, to say they don’t have the ability is naive IMO, they can get the ability from Russia or China.
Fortunately those countries don’t have those capabilities and Russia and China are not about to give them those capabilities, and just because they are sublaunched and only kills half the US population is not a prescription against Argmageddon against the perpetrator and for something like that we would know who the perpetrator is.
The defense is that the perpetrator gets whipe off the face of the earth. Period. No equivocation. No ifs ands or buts. Period.