Re: As I recently wrote on the broad matter...
>if the response before any missile is even half way across the Pacific will be to flatten them.
Geez, I sure do hope that, if both the West and the Soviets managed to live with a doctrine of "take first strike, then respond massively" during the Cold War, then everyone is sane enough not to launch a nuke towards NK until you know what they've launched.
The reason this was done is because false alarms happened several times during the Cold War and the stakes were immeasurably higher than Fat Boy's little tantrums. It doesn't make any sense to be on hair trigger, both the US and Russian arsenals are designed to survive strikes orders of magnitude bigger than NKs and hitting back right away doesn't stop the incoming missiles in the least. That's why both parties agreed to sit out the first strike.
Factor in that China might be mighty peeved, or worse, panicked, on seeing a US counterstrike and you can bet the counterstrike is gonna wait. All this, of course, is assuming some level of rationality out of POTUS or, failing that, in the NORAD protocols.
This whole thing about the EMP threat is highly uncertain as well. Yes, it would cause damage. How much? No one is quite sure. Again, even during the Cold War, the EMP was never quite that clearly the end of things (granted, standard atomic war would have done that quite well).
Here's a blurb about that: https://www.bloomberg.com/news/articles/2017-12-22/hardening-power-grids-for-nuclear-and-emp-attacks-by-north-korea
The 20KT cited by Big John is likely to be more correct than wrong - NK's are for now fission bombs and those top out in yield rather quickly - with bomb damage falling off at square of distance, Hiroshima type damage on any one selected target in Hawaii would be expected, not total destruction of even one of the islands. I'd aim for Seattle instead if I was him - Honolulu et all are not big cities.
Another issue for poor Fat Boy is that no one really knows if the various US Star Wars ICBM defenses would work. They might. Or they might not - their tests have worked at times but no one is sure if the tests were representative of real world difficulties. If they did work, he'd be flattened and wouldn't have caused any damage.
And, currently, it's not even a 100% certainty that a NK strike would actually work as intended.
It makes more sense for him to hold on to his missiles and use them as a threat against invasion or a regime change situation, rather than just lobbing them for the hell of it. He can even enlist them in his usual gambit of taking Seoul's population as hostages.
He might be a lunatic, but his dynasty has lasted 70 years so far, they're careful in what they do. Unless his back is seriously to the wall, these missiles are only useful as long as they are unused.