I have always felt like North Korea is not what it seems. Best guess is they are an arm of China, Russia or Iran and it's easier to agitate us from NK instead of the direct country. I suspect our military knows exactly who is running NK behind the scenes and Trump's tweets are a playful way of calling them out.
What would I do? I would keep sanctioning NK and drying up their money supply. If China and Russia or others help NK, I would do more of that against those countries. If NK lobs a Nuke, I would glass the place.