The people who cost the Democrats in 2016, 2022, and 2024 and have greatly hindered their success in 2018 and 2020 are the hard left who infest lemmy.
Apolitical people are a non factor since they never vote and independents aren't either because the margins of those who don't lean one way or the other is very slim. The sabotage in the left is internal. The center left is corrupt, the moderate left is incompetent, and the far left is a tumor that gives MAGA a run for its money.
Things won't change unless the moderate left rejects the far left from their ranks, actually organizes and mobilizes to go after corrupt center left politicians, and try to come up with messaging that appeals to the general public and not just themselves. There's potential for real change, but it requires a lot of effort.