"...prompting the threat of a "massive" military response from the United States if it or its allies were threatened."

Empty bombast. Why?  Because Japan, South Korea and North America are ALREADY threatened, almost as much by empty rhetoric such as this as anything else.  

Enough already.  Simply don't issue any response to anything NK does.  

Just be ready, and when NK least expects it (because there is no American rhetorical response)...strike.