Patience, grasshopper.
We're not just jumping in there with guns blazing, because of the number of U.S. troops and dependents, and innocent South Korean citizens, who live near the DMZ and who could be wiped out in the first wave of an attack or reprisal by North Korea (it's personal to me, since I have relatives among them).
We'll get to it, it just has to be done carefully. The threats are annoying, but as long as they are still talking, they aren't hurting anyone...and the regime is getting weaker and weaker.
We are walking a tightrope here, however.