She supported Jill Stein, especially in Pennsylvania where Stein's votes were the difference in 2016. She also then went on CNN after the fact and basically laughed at the Dems for losing...
It isn't her policies, they are excellent. It is her rhetoric and her "fuck you its my way or the highway!" attitude. Think back to the last 2 Dem Primaries, it wasn't Bernie who was the issue it was the people who spoke for him and their "we would rather burn the house down than work to fix the house" attitude which ultimately did him in. To them (and her) it is purity above all else. Letting Trump take power to prove a point is more than fine with her and her staunch supporters, and losing is not an option. The system is corrupt...except for her of course.
Look, it is completely hypocritical to mock Trump and the GOP for claiming his loss was "rigged" and "fraud" with "outside interests pushing an agenda" and then not call that out within our party. Turner has all the right ideas but she is just the way wrong person to implement them. The proof is that she couldn't just accept that she lost, it had to be dark money from outside interests that took her down. (just like when Bernie lost to Hillary) She stokes the same firebrand BS that Trump does only she does it for our side so we should just accept it. Screw that noise. She is a power hungry POS who thinks that both sides are so corrupt only she and her kind can fix it. (sound familiar) If she can't win she was obviously screwed and now she and her ilk can just take their ball and go home. The amount of parallels between her and her sycophants and the Trumpers (again not policy, attitude) is rather scary.
The Far Left can do way the fuck better than a turncoat proto-authoritarian. Cori Bush is 100000X better than Nina Turner could ever dream to be. Brown is not perfect, but she holds the Dem Agenda (and the Agenda of all under the umbrella) as her own unlike Turner who would sooner light herself on fire than side with Biden on anything.