Second, Latinos, who are key to the outcome in several crucial states — Arizona and Florida, for example — have shown less support for Biden than for past Democratic nominees. Many Hispanic voters seem resistant to any campaign that defines them broadly as “people of color.”

Third, absentee voting is expected to be higher among Democrats than Republicans, subjecting their ballots to a greater risk of rejection, a fate more common to mailed-in votes than to in-person voting.

Fourth, the generic Democratic-Republican vote (“Would you be more willing to vote for a Republican or Democratic candidate for Congress?”) through early July favored Democrats by more than 10 points, but has since narrowed to 6 points.

Fifth, the debates will test Biden’s ability to withstand three 90-minute battles against an opponent known for brutal personal attacks.