There's a difference between imprisoning someone when there's a shadow of doubt, and not voting for someone when multiple, concordant lines of evidence suggest the dude might be a rapist. And that on top of easily a dozen other, fantastic reasons why this person is ill-equipped to hold any office whatsoever.
Blackstone's Formulation applies to governments and legal systems and jails. It's not something that should always govern what you think or support. For instance, Bill Cosby shouldn't go to jail because there's no hard evidence he's a rapist, but to anyone with even a modicum of common sense it's pretty obvious.