About the west coast, I was thinking of the submarine launch technology, or even just floating a nuke in on a freighter.
I’m less worried about a NK sub, pretty sure our SOSUS listeners would pick that up and kill it, but smuggling a suitcase bomb or worse in a container on a freighter - definitely plausible. I try to not subscribe to the Fear Merchants, but if you haven’t read One Second After by William Fortchen, it’s worth the read. Wouldn’t take much of a missle to light off an EMP strike.