They've demonstrated the capability of probably being able to hit the West coast of the continental US with a missile; they also have some nuclear weapon capabi

They've demonstrated the capability of probably being able to hit the West coast of the continental US with a missile; they also have some nuclear weapon capability which may or may not be a true "hydrogen bomb". I don't think anyone outside of N. Korea knows what their exact capability is on any particular day -- which is probably exactly what they want. There is a realistic concern about the pace of their developments, though, which is IMO the real food for thought. Most analysis from more than 12 months ago did not assume they would make the advances in missile range or throw weight that they have, which raises concerns that another state is helping them (actively or inadvertently). If that is the case, they might also be able to miniaturize their weapons more quickly than originally estimated as well. Absent some outside factor, it's safe to assume that at some point in the not too distant future, they will get the combination of weapon mass down, and missile throw weight up, such that the two meet and give them enough range to hit the continental US. Most arms control theories suggest that it's better to be clear about what your responses will be to particular stimulus ("deterrence signals"), in order to reduce the threat of an accidental war. IMO, if the US leadership was more competent or even credibly sane, the best-possible response to N. Korea would be a system of "red lines" composed of DPRK actions and pre-planned US reactions, in consultation or at least full view of other nuclear states (principally China and Russia; the South Koreans would hopefully have some say over the responses, although they might do well to distance themselves). I've read some essays that suggest there was an understanding between the US and USSR in the 80s regarding Libya to something like this effect. But of course, the US is not really credible at the moment in terms of internal consistency or rational behavior, which makes rational-actor game theory, on which a lot of deterrence is based, difficult.