So, on the face of it, Trump's threat to bomb North Korea if it so much as looks at us crosswise seems... weak. A rational person would have put out an obvious and hard deadline, such as actually launching a missile or test, rather than merely looking like you might. A smart person would never have boxed themselves in on a bluff they didn't want to be called on. A mildly competent person would not have promised to start a war over imaginary weapons of mass destruction, particularly after having spent so many years complaining about the last one.
Despite all that, is mere incompetence and narcissistic nilhism really sufficient to explain this latest move? Particularly as it comes on the heels of President Xi of China's visit with Trump, which apparently included an education on Asian geo-politics. (So nice of China to educated our President for free! I'm sure they did it entirely out of the goodness of their hearts, with no ulterior motives at all.) And following the impulsive attack on Syria, it looks doubly suspicious.
Here's my idiot conspiracy theory for the day: Xi put Trump up to it. Now Xi is sending more diplomats to NK to tell them, "The Americans are insane - they might do it! You need our help to defuse the situation." They are playing good cop/bad cop, and they tricked Trump into being the bad cop.
If it works - great! The Chinese get to squeeze NK a little more, peace gets restored, and things go on as before but with China in a better position. If it fails - it is entirely on the USA. Trump either backs down from his empty threat or worse, carries it out. We get either massive collapse of international prestige or an actual war that will kill millions. Either way the USA is made a fool; in all cases China's position is only improved.
This, my friends, is the work of a Great Negotiator.