It seems to me that Biden’s shoulder rubs and hair-smelling, won’t sink him. It’s weird and inappropriate behavior, but not sexual or malicious.
(There’s some doubt out there about the specific Lucy Flores story by the way, even if it seems plausible enough):
https://twitter.com/mattyglesias/status/1112414137441796103
If Biden routinely crossed the line into honest-to-goodness groping, though, it’s inevitably going to come out and will end his proto-campaign or actual campaign in short order.