Long time frenemies the PRC and Russian Federation have had a checkered history at times standing United against America and at times coming to arm's against each other(ie; Ussuri border skirmish).
Ongoing today the frenemies have extensive trade ties which has helped Russia defy sanctions over it's invasion of Ukraine while currency swap agreements have reduced their dependency on the dollar. Militarily and politically the frenemies have formed an implicit pact to support the other in most instances such as joint naval drills in 2016, China's increasing support for Russia in the Crimea, and Russia's support for Chinese projection into the South China Sea. But despite official declarations of goodwill Chinese-Russian relations have been limited by mutual suspicions, pricing concerns, inadequate transportation infrastructure, and competition for influence in central Asia. There is great potential for the relationship to go either way but what would be in your opinion be the best way to drive a wedge between Russia and China for America?
Of course somethings, such as Russia's need to diversify mineral and energy exports and China's desire for them won't change barring large upheavals and some level of interaction will occur regardless.
Other things, such as the Post-Tiananmen Square EU arms embargo driving China towards Russia for its military supply might be a bitter pill to swallow but like Saudi Arabia might be seen as worth it in the State Department.
Its easy to say crazy or stupid guy takes over Russia or China, but a more constructive challenge is what the Americans could've done different. Maybe we'll learn something about American foreign policy this way.