There actually is surprising cohesion in the Dem Senate caucus right now (relative to the past). There isn't room for someone to just be a "Max Baucus." If you want to stand out as sticking it to the hippies you gotta go Manchin or Sinema, and that's what Fetterman's doing.
And while we're in "yelling at voters" mode, this is relevant:
If you’re a Democrat worried about the 2024 election I think one really bad thing that could happen is if a high profile senator in a swing state who got elected by galvanizing the progressive and youth votes starts actively antagonizing them and confirming that he played them.
— Ghost of Toyotathon Sales Event Past (@PanasonicDX4500) December 18, 2023