His explanation: "China is a peer competitor for the US" so it needs not only be contained but be "rolled back".
Whilst Russia is not powerful enough to threaten the US so it makes no sense to get into a proxy war against it. In fact, the US should ally with Russia against China
However, how can you condemn something which he says is so dangerous it can lead to nuclear war whilst supporting another?
Logically speaking, the only way he could say that is if he believes that the risk of nuclear war is worth it to deny China regional hegemonism in Asia.