Nah. Lack of communication really. The North Koreans are intimidated by the US-South Korea military drills, and may even erroneously suspect them to be disguise for a real attack (North Korea did this themselves to start the Korean War). Meanwhile the US is not going to go away as they have to reassure South Korea they are with them, so you'll have this continued sabre-rattling.
Also the new leader has to make himself look militarily capable. The US doesn't need to do anything else other than keep a presence, even North Korea can't be dumb enough to attempt any kind of missile attack.