It's not Dems fault for not "quashing" ideas or narratives. I mean, how do you propose to do that exactly? Tell people it isn't true? How well has that worked in the past.
We've been trying for a century to quash the ideas written into the "Elders of Zion" hoax, and we don't seem to be all that effective in doing so. We have neo-Nazis in the US. Hell, Germany has neo-Nazis, or their equivalent.
When people are motivated to believe something, especially when that thing absolves them of responsibility for their past decisions, it's hard to quash that.