NK doesn't pose a threat to the US, they only pose a regional threat (mainly to SK). The pride of their air force is a few Mig-13's from 1950 or so. Nukes wouldn't be necessary, we would have complete air superiority within 24 hours at most, and the only thing they would be able to do is destroy Seoul with artillery before we could stop them (they can easily do that, also no nukes required, and even old artillery is still artillery).