The exact same thing happens every year, and did so when Obama was in charge too. US & SK do war games in the area, NK throw a strop and whinge, war games end and everything calms down again. The only difference this time is that Trump isn't known for being calm under pressure
Realistically nowt will happen, no-one will push that far as NK know they'd be wiped out in seconds and they don't really have the ability to hit anything other than SK. Fatboy Kim has the most to lose, and he knows it: He'll only ever be a mouth and def no trousers.