The biggest problem between Russia and China is likely going to be Eastern Russia, including Vladivostok. This region of Russia was historically China, and Chinese immigration is happening at such a pace that it's estimated by 2030 the Chinese will have a majority in this region. That spells trouble for their relationship. China will want that land back, especially if it is majority Chinese people. And Russia will not be willing to give up their only year round ice-free port on the Pacific.

This is less than a decade away, it's the not-too-distant future. Russia is getting weaker while China gets stronger. And if China becomes stronger than USA, then it may well be in our interests to be friends with Russia instead of enemies to ensure the geopolitical balance of power doesn't swing decisively in China's favour.