North Korea will not directly attack the US with nuclear weapons. If they did, the huge distance across the Pacific Ocean would provide plenty of time to detect an ICBM and shoot it out of the sky.
What they could do, however, is attack our lesser defended allies or assets, like South Korea, or maybe the Aleutian Islands.
However, I have complete faith that if North Korea uses nuclear weapons, that the US will not retaliate with our own nukes.