we do not have anything remotely like a consensus white-knight replacement for Biden waiting in the wings.
I doubt that Biden believes Harris would have a better shot against Trump than he would; certainly the polling doesn’t support that.
He did not seem like a man inclined to step aside.
*should* Biden step aside? well, that depends on the alternative.
If there was good reason to believe he’d lose to Trump and him stepping aside would result in a W, sure.
The polling argument for that is nonexistent. Maybe it will exist now.
The immediate result would be either a consensus Harris ascension, which I have no confidence we can pull off for some pretty good reasons and some pretty bad reasons, or a contested convention in Chicago
so you wind up having to make this involved bankshot argument where, sure, nobody polls better but Harris is well-known and these other people who also don’t poll better aren’t well-known so they could grow.