Had this been a Republican, namely Trump, the media, or most of it along with his opponents, would be clamoring for Trump to get out of the race or resign due to his laying hands on this girl. They wouldn't let the story drop for weeks if not months or for ever.
To me, this isn't disqualifying for Biden but it does reveal his not ready for prime time campaigning and continues to be a problem for him. Realistically I don't see any of the current group of Democrat contenders that will be able to control and take the stage against Trump in a debate format.