Re: Missing the point?
"They so much as threaten such a thing the regime will be over within a week"
Absolutely. MAD (Mutually Assured Destruction) doesn't apply here. They could seriously damage the US (or South Korea) with a kludge nuclear device. But only damage. They wouldn't be able to knock out anybody. And retribution would be complete and justifiable in the interests of self defence. Indeed if NORK attacked the US I bet the Chinese would be in Pyongyang before the POTHUS could press the button. They certainly could not entertain a neighbour prepared to use weapons. Only to play with them.
Willy waving in extremis.