You’re opening up the proverbial worm canister. You and I may know that Sanders is likely to never have committed an act of sexual aggression / harassment. But anyone can allege that he has, and for all we know, that hypothetical person may have prepared to do so by “informing” someone else before reporting the bogus allegation. That hypothetical person may also have been coached into appearing genuine.

So replacing Biden with Sanders is no guarantee that there won’t be similar charges against Sanders.

If you’re going to replace Biden, the more foolproof strategy would be to do so with a woman (there are relatively few cases in which a female elected official has committed sexual harassment, and as far as I know, none in which a female elected official has committed some form of sexual assault). Plenty of qualified women to choose from.