I don't think it's against US interests for China to sell weapons to Russia. Post-WW2, the traditional way in which powerful nation states test their conventio

I don't think it's against US interests for China to sell weapons to Russia. Post-WW2, the traditional way in which powerful nation states test their conventional (non-nuclear) capabilities has been through proxy warfare. The US would probably love it if China sold some of their weapons to Russia, so that US/NATO equipment can be tested against it. Conversely, the Chinese would probably not mind testing their "on paper" capabilities "in the field". The caveat here being that the US can probably upgrade/adapt to whatever is learned about Chinese equipment. In other words, there is no substitute for actual operational experience, and both sides benefit from selling weapons to the various parties in Ukraine, in order to get said experience.