China should be upset over North Korea for deeper reasons than on the surface. Trump's "fire and fury" comment a few weeks ago was the clear explanation.
Donald Trump was not in favor of the W. Bush invasion of Iraq. Trump does not like large footprints of war. If this administration authorizes action in North Korea, it would not be anything like Iraq. It would be surgical and instant. There might not be time to react.
With the threat growing from China's venture missions—flying its flag on man-made islands since it can't find other ways to fly its flag on more soil—the Pentagon would be foolish not to seek an opportunity for a small demonstration. By not bringing North Korean threats to an absolute halt, China may be giving the US just that opportunity.
China and Russia neither want North Korea to be volatile nor shut down. Perhaps they don't understand North Korea's political DNA. It seems they all want to have their cake and eat it too and blame the world if they can't, a mindset common in Communist regimes.
So, Communism itself is on trial, for its ability to deliver on its goals. But, so on trial also is Democracy's ability to respond if Communism fails to deliver.