Relations between the USA and Russia have not been very good since the end of the Soviet Union. Instead of a rapprochement between the two great powers, the mutual attitude has been characterised by confrontation, a circumstance which benefits a third power in particular.
The triangular relationship between Russia, the USA and China underwent a considerable change almost exactly half a century ago. Under President Nixon, the United States ultimately succeeded in exploiting the tensions between the two communist empires and using smart diplomacy to play China off against the Soviet Union. This gave the US a decisive advantage in the Cold War, which two decades later was clearly in its favour.
The central aspect of this strategy was to maintain closer relations with each of the two states than the other two had with each other, i.e. that the Soviet Union was strategically more closely tied to the US than to China and that China was more closely tied to the US than to the Soviet Union. This made the United States the central actor in this group.
After the West, and the US in particular, idiotically adopted a confrontational stance towards Russia for over two decades, China is currently the strongest player within this constellation. But it does not have to stay that way.
There is enough potential for conflict between Russia and China that the US could exploit. They would only have to be ready for it.