Biden might say the wrong thing at a debate, or have an awkward moment in an interview or at a press conference. Trump’s massive advertising campaign might begin to resonate, hurting Biden’s favorability ratings. Biden’s campaign might make poor decisions about spending allocations in the battleground states, or the coverage of his campaign may sour if he loses even a percentage point or two in polls. Presidential candidates with large leads have all suffered from less.

And then there are the factors outside of Biden’s control. It is possible that Trump before November will announce a coronavirus vaccine, whether real or imagined. And it is possible that the economy will improve, a prospect Republicans are pinning their hopes to…

Late this week, Les Francis, a Democratic strategist and former deputy White House chief of staff in the Carter administration, sent an email to a circle of friends, including a former congressman and former administration officials, with the subject line, “123 days until the election — and a sobering prospect.”

Right now, he said, “Trump is more than vulnerable.” But then he went on to outline a scenario in which Republicans hold down turnout and sufficiently harden Trump’s base.