I think this is going to play out worse with voters than the Democrats think.
Even taking the facts as alleged, this was a drunk 15 year old, and a drunk 17 year old at a party. There was no rape, her clothes didn't come off, there was no touching of her genitals, etc.. There is no evidence of physical harm at all. I think a lot of people would be hesitant at holding that against a 17 year old for the rest of his life. And that's if it was true.
I think a lot of ordinary people probably thought it was pretty weak to bring something like that up 36 years after the fact, and not be able to provide any details to corroborate the story. There would have been a lot of skepticism there, and I think most would have sided with Kavanaugh. But when the GOP offers her a chance to testify and she refuses....All but the true hardcore are going to start thinking "this was bullshit all along."
The Dems just gave voters a little taste of what things would look like if they were running Congress. I don't think that's going to help them come November.