You said everything I was going to say, and far more eloquently than I could have. Japan is not so much a threat but rather a hand of the US, and any sane people there would much rather have economic cooperation. Without US instigation Japan will eventually crawl back inside its shell, the way it did centuries ago. Advocating genocide is not only morally uncalled for, it is irrational and counterproductive.

Mongols and Manchus have been Chinese since accepting the Mandate of Heaven, or even earlier (Nurhaci and other Nuzhen leaders were ennobled by Ming)

Another Trumpian populist president would probably only further divide the US public. Even old Joe Biden is very... triggering for those citizens who opposed him in favour of Trump. As long as Americans hate each other more than they hate China, there is not so much cause for concern, but China should build op strength regardless. Even if the US were to suddenly collapse into warlordism next week, the resulting unstable situation would be dreadful for China.