Aren't there Olympic games scheduled in South Korea this year?
(I don't follow the Olympics, couldn't care less, really)
I'll speculate that any action Mr. Trump wants to take will have to wait until those games have concluded -- perhaps involving a last-ditch effort to get the Chinese "on board".
Having said that, if we were to take some kind of limited action against the Norks -- and pull it off -- this would guarantee a second term for Mr. Trump, and notch America's position in the world upwards a few steps. And push China down a bit.