If the best the Democrats can do is serve up rehashed ‘Russian collaborator’ allegation not supported by any evidence, there’s only going to be one outcome. And this is The White House will not be getting a new tenant in 2021.
If the Russian interference narrative could not save Hillary from being Trumped in 2016, it’s not going to work to discredit Bernie and put up a more establishment friendly candidate in 2020, particularly as Putin is portrayed by liberals as a right wing figure (if we take right — wing to mean authoritarian, they’re right, but that’s not going to help associate Bernie Sanders with him.)

If they want to wing they have to find a credible candidate. And it looks like if one emerges the DNC will take him or her down in the Primaries season.