As military threats go, it's as close to insignificant as they come. Stratfor would tell you that an American carrier group is nigh impervious to even technologically advanced enemies like Russia. This isn't to say it can't be taken out. But NK has almost no chance of conventionally attacking a US carrier group with any chance of success. You should read up on what goes into a carrier group's defense. You'd be rather surprised.
It's much more likely we'll sink some less expensive U.S. war ship ourselves, something cheap and obsolescent. We'll claim North Korea did it. Then, to use Trumps terminology, we'll bomb the shit out of North Korea. That worked for us in Vietnam until someone ratted on us years later. Our "clever" trick used to invent an excuse to bomb Vietnam turned out to be a bad idea, but since when have we not followed up on bad ideas?
Yes, and I'm sure Mike Tyson is quite concerned with the possibility of Richard Simmons hitting him in the face.