From his Wikipedia page, Joe Manchin appears to be a Republican pretending to be a Democrat to get elected in a state that is solidly Republican, but has returned him since 2010. He gets huge majorities in his primaries and thin majorities in the actual election and then in the current session has basically appeared to block all significant Democrat policy, but doesn't seem to be drawing significant removal attempts from either side.
Why is Joe Manchin a Democrat when he sides so consistently on significant votes with the Republican party? Why do Democrat primary voters in his state vote for him so strongly, or even consider themselves Democrats if they consider him to align with their positions? Why does the central Democrat party continue to support him? I assume all of this has an underlaying unifying cause, but I have no idea what this might be.