Let's be honest. The only reason US backed down from North Korea b/c it already has WMDs and also NO natural resources. Whereas Iraq, who doesn't have any known WMDs, has a least a slingshot full of mustard gas and anthrax...not to mention, sitting in a desert filled with oil.
America will never send troops en masse unless the place they're going to has serious resources: oil in the Middle East, diamonds in Somalia, etc.
Korea, north or south, doesn't have the natural resources that the US craves for.
It would an unforgivable and maybe an impeachable act if Bush Jr. did start something in Korea, and putting the world on the brink of global destruction for the sake of control of all the Daewoo speakers, Hyundais, and microwave ovens to shake a stick at.