To steel man their argument, it's not about the polls now, it's about confidence in these candidates to fight into a lead. Harris doesn't look any worse than Biden here, and I think she'd have more ability to prosecute the case, so to speak.
That said…
The only way to make this situation worse is to give Trump the ability to say "I punched him so hard he had to quit the presidency in shame, and they had to send out their second string"
Right, and since no one hits 50 percent in any of these polls, it’s also about how the undecideds will break at the last minute. The Democrats need someone who can make a strong closing.
The evidence of the last 3 days is that Biden can make a very strong closing if he has a cheering crowd and/or a teleprompter and/or the adrenaline of a near death experience
What if the problem is that Dems in general are blamed for "bad vibes" (i.e., post-COVID malaise)? Then swapping Biden for somebody else won't help, but you lose the advantage of incumbency.
