Spoiletta: I don't think that the person that asked the question you referenced understood the President's implications. - What could possibly be tougher than the threat of blowing NK off the map? (Hint)
The President's reference to fire and fury in his initial threat to NK is an allusion to President Trumpman's message to Japan before dropping the bomb.
It is an axiom that if NK tried something, the US would act exactly the way the President said. NK knows this even if the President hadn't said it, so there is nothing extreme about his initial message. NK has continued to make threats against the US. The president has made it very clear to NK what to expect. The only thing tougher than a threat is not another threat but actions that speak louder than words. That's is how I interpret the President's message.