More importantly they have a HUGE population to conscript soldiers from and over 5 times the industrial capacity of the USA.

We would lose a war with China, badly. We could nuke them but then the world would turn on us after the Chinese nuked us.
We can't win.

Thats what most of you are missing. The US HAS NOT won a war since WW and in my opinion we lost that one BIGLY because we fought for our enemy.