Even if they do have weapons of mass destruction, their biggest ally seems as if they'd rather side with us than them & the country is so god damn small & poor, a good surgical strike at, say, a public rally could take out their entire government at once.
Of course, the problem is the devotion of the people & the remains of the military would probably start a nuclear strike if it happened, so you might have to identify their WMD stores & drop teams in to seize them at the same time as the attack.
It wouldn't be an easy strike to manage, but NK could theoretically be conquered in a day or two. In other words, threatening us is not putting them in a good position.