Diplomacy without a credible threat of force is of little use in dealing with the DPRK, which is determined to make itself a nuclear power.  The North Koreans have a real fear of attack, which massive yearly US/ROK military exercises offshore do nothing to ease.  They are not gathering weapons in order to trade them away, but rather as a means to security.  The Kim dynasty is paranoid but not stupid, and its longtime grip on power shows there is a logic to its actions.

If the US has decided not to allow a missile threat to the homeland, a limited strike would not be wise.  The North would surely retaliate, perhaps by attacking Japanese bases as a way of stirring up Korean nationalism.  Then what?

Iran, another threshold nuclear power, is watching carefully.  One possible approach would be to start a serious military buildup.  This would concentrate the minds of the Chinese and put the ball in the Northern court.  But of course the whole situation  is very dangerous.