A few thinks here.
74 introduces a new complication as concerns ability to respond. Any attack, be it nuclear, emp, conventional or otherwise would likely be preceded by a cyber attacks as he suggested, The Chinese, and likely others too, have gotten very good at this, and all of these successful intrusions we keep reading about are part of their testing and debugging efforts. The recent media reports of that malware that is is everywhere in our systems is most assuredly there waiting for WWIII to commence.
As for limited nukes, if the big 3 (US, China, Russia) are involved, it could not possibly stay limited. If the smaller players go at it, then maybe it could stay limited so long as the big 3 stay out of it. Not sure whether they could though.
If North Korea or Iran could EMP us, I suspect they would, even if it wasn’t nation-wide. North Korea likely wouldn’t care if we knew it was them who did it. Iran would likely launch from off one of our coasts and then scuttle the ship as part of a suicide attack approach in hopes of it not being pinned on them. Hopefully the NSA still has time to spy on someone other than US citizens and would know Iran was planning something like that, but who knows anymore. An EMP is my biggest fear.