Which party benefits electorally from Breyer's retirement?

[America Needs a 13-6 Progressive SCOTUS]

The West Virginia Republican Party (in 2024)

An expectation that Manchin would vote for any Democratic SCOTUS nominee would be priced in to the WV-SEN 2024 result even if no SCOTUS vacancy were to occur. Based on this, Manchin will not be measurably worse off after voting to confirm a replacement to Breyer, and will only be doomed to an equal level as he was before.

[America Needs a 13-6 Progressive SCOTUS]

The West Virginia Republican Party (in 2024)

An expectation that Manchin would vote for any Democratic SCOTUS nominee would be priced in to the WV-SEN 2024 result even if no SCOTUS vacancy were to occur. Based on this, Manchin will not be measurably worse off after voting to confirm a replacement to Breyer, and will only be doomed to an equal level as he was before.

I disagree. Manchin's pretty good (under these circumstances) approval ratings are because of his moderate image and the tons of articles effectively promoting him as someone who won't just back party line. Voting to confirm a justice who will be labelled as far-left by Republicans will hurt this reputation for him.

He already voted against Barrett though. At that point, the damage was done to his ability to run in 2024, and you are not doing additional damage by having him vote for a Dem nominee. That said, the writing was blatantly on the way for Manchins re-election campaign in 2024 from the moment after the 2018 results came in, so its not like he had a chance that he would be giving up anyways, and I do not believe the poll showing him above water in West Virginia to be at all accurate anyways.