Trumps only tactic for any problem is threats and bluster.   Of course it's all done out in the public so everyone can see how tough he is.  He's not bright enough to consider other options.  

But he's boxed himself into a corner since the threats aren't working and the u.s. says they won't start a war.  

It's the North Koreans who are the wild card.  Would its leaders actually be stupid enough to attack?  They must know that whatever damage they might inflict short term,  it would be the end of their nasty little tinpot regime as well as their own lives.  

For the record, I think the solution is still sitting down at a summit with the Chinese and the Russians, ask them what it is they'd want to cut off the NK regime and then negotiate from there.