I've believed for years that NK is really doing China's bidding, China's propping up the NK regime and China would like nothing more than to see the USA get hit by a nuke, whether in Alaska or on our West Coast.
That will give China the opportunity to do what they want/need to do which is secure natural resources elsewhere in the world that it needs, without fear of US retaliation.
That's my belief/opinion of course and I could be completely wrong.
I’m not sure that it makes sense for China to want to see us nuked. The U.S. “is” their economy. If all trade with China is stopped they would collapse financially.