Please cite your source for that? My understanding, based on studies like the one discussed here, is that misinformation does tend to be concentrated along partisan extremes. https://www.npr.org/2021/03/06/974394783/far-right-misinform...

That said, it's absolutely true that it wasn't just democrats pushing the idea that bernie sander's was cheated. It was also russian disinformation campaign. https://www.wired.com/story/bernie-sanders-russia-chaos-2020...