IMHO Kim Jong-un is all talk. He's sabre rattling to see what he can get. He'd only attack if he felt he was personally in danger. Trump is right, the NK situation needs to be dealt with and his initial approach of pushing China hard is appropriate.
American Admirals are not stupid. They will not place the Carrier Battle Group close enough to NK to put it in harm's way. Neither the NK air force or surface Navy are much of a threat, although I guarantee CAPs and AWACS have been doubled. The fleet certainly won't be letting any civilian ships within 20 miles. The NK submarine fleet is a potential threat as they have quite a few fairly modern diesel boats equipment with Chinese sensors and torpedos. American CBGs have already been shown to be vulnerable to diesel subs. Kim has nukes, but limited delivery platforms .... but I just can't see him using them unless he felt assassination or invasion was imminent.
Having the USS Michigan making a port visit in SK is interesting. Michigan is a SSGN that carries ~150 Tomahawks. Normally a missile boat would NEVER EVER come to the surface in hostile territory, especially without close support from destroyers or cruisers as they are defenceless in port, on the surface or in shallow water. I think this was a stop-gap until the CBG got closer.