The smartest Foreign Policy, and specifically North Korea, scholars will tell you that Trump's twitter antics have actually been quite an asset in dealing with the current regime in North Korea. We have had plenty of the typical FoPo wonks swing and miss at getting NK to halt nuclear progress over the past 25 years. This administration is the first to not be laughed at and taken advantage of. While I don't think this strategy would work with many in the international community, it seems perfect for NK.
We've given the bully detention, suspension, and taken away his lunch money. It hasn't helped. At some point you need someone to walk onto the playground and let the bully know he isn't the only one in the school willing to throw down.
Austin Bay from Strategy Page explains the
deliberate strategy behind all of this here, via The Observer and Real Clear Defense -
http://observer.com/2017/08/donald-trump-north-korea-diplomatic-military-strategy/.
As an aside, Real Clear Defense is a must scan if you have interest in the current US/Asia happenings. It curates Defense and FoPo articles from a broad ideological spectrum and finds all of the best sources and sharpest minds in those areas.