Regardless of Trump's belligerance and bullyism, cooler US heads need to take control.  With Trump sidelined NK is not going to start a shooting war and the US would be ridiculous beyond pale to do anything that gets hundreds of thousands of South Koreans killed

N Korea is never going to give up what they have.  They dont trust the US (and Trump only reinforces that-who would want to negotiate with someone who is likely lying) 
By all means mean a defensive shield that works but focus on talks. 
The real threat is that N K decides that terrorists might provide hard currency for some nuclear stuff.   Then we are really in trouble.
Negotiations need to focus on making N Korea feel their future is secure (ie; end the Korean war) and on getting security around their nuke supply.
Evn Russia poses this same risk  I mean Pakistan has nukes and they live right beside the Taliban and remnants of AlQaeda