I think we've identified it: it's the point at which these two things become more likely than not.
1) Facts emerge that make it likely a court could rule that Hillary Clinton is disqualified from ever holding any further public office.
2) The party gets some comfort with the emerging Biden ticket.
Get comfy, killers. You may be about to watch the destruction of one of the great powers of our age pour encourager les autres. Whatever comes after, it's going to be a tremendous spectacle.