I don't think there's much chance that the North Koreans would attack Guam or any other territory out of the blue. They would only counterattack if they felt existentially threatened. The questions is, At want point will North Korea feel it is threatened enough to make such a strike? We don't know that yet.
Violence has always been implied by previous US presidents: That is to say, if North Korea launched an attack, or crossed certain red lines, they would be met by devastating force. And this has been said even by people in the Obama administration very recently. But the kind of rhetoric that Trump is using is different, and I think probably not helpful, because it just provokes the North Koreans to ratchet up their rhetoric as well. At this point, it seems that we urgently need calmer heads on both sides, and we're not getting that.
Obviously, the US does not want a shooting war with North Korea. But there has to be some path out of this situation that is also presented that is peaceful. We have sanctions, we have deterrence, but the third leg of any resolution to this problem has to be dialogue. It seems prudent for the US to not only threaten North Korea, but to also offer a way forward.
The concern we should have is not that North Korea would suddenly launch a preemptive strike on Guam or any other target, but that the conflict escalates to the point that there is a miscalculation on one side or another and missiles or bombs are dropped.
