Noth Korea serves a greater purpose to the US. I do not believe they want to take out the leadership of NK at all. In fact, there are valid arguements that NK is a CIA proxy state. 

Without North Korea, the US has no reason to have a massive military presence in South Korea. Without the phony North Korea threat, the US has no legitimate reason to maintain massive military bases in Japan and elsewhere in the Pacific (around China). Here in Australia, the former Gillard government allowed the US Marines to establish a base in Darwin in the Northern Territory. We will never get rid of them. 

The reason for eastablisng the base? Primarily, the North Korean "threat". 

Remember ... Kim Jong Un was educated in the same elite schools as your average run-of-the-mill elite NWO Globalist, UN beauracrat & Wall St bankster.