This has been a known quantity for decades. It is why we harden our military hardware. Our adversaries know our gear is hardened.
To ponder that anyone can simply launch an EMP attack upon the U.S. and “get away with it” is absurd (assuming we don't have another pussy POTUS like our 44th). It is one reason I tend not to worry about EMP attacks and categorize them with “the end of civilization” scenarios.
military hardware hardening doesn’t matter in this scenario. Nationwide loss of electricity will result in approximately 90% death rate in the US.
So if NK launches a successful attack, we glass over the country. but that leaves the govt totally overwhelmed by civilian disaster of huge scale. no amount of military hardening can mitigate that.