Nothing that fits into the category of ‘scandal’ could get me to vote against the Dem nominee.
What could get me to vote against the Dem nominee: they’d have to demonstrate somehow that, as President, they’d likely be even more of a disaster for America than Trump is.
What could get me to simply not vote: if the Dem nominee committed an extremely serious crime. But in that case, the party would surely declare its nomination null and void, and nominate someone new. So I doubt that’s really a possibility that a voter would have to reckon with.