Heh. Sure about that? The only pol in the democrat party with lower ratings than Biden is...Harris.
Were Joe to step down for health reasons there's a 0.0% probability she'd be the top of the ticket.

She has poor ratings, but she's the Veep. So she has a powerful claim to be Biden's successor, both metaphorically and having first crack at the campaign apparatus and the $200+ million war chest that's already been built for the re-election run. She's already on the ticket. She's already campaigning for national office. It's already the end of January - no one else in the party could assemble a national campaign organization or anywhere close to that kind of money in enough time.

Again, all this speculation ignores the realities of what's required to assemble a modern Presidential campaign. It's not something you can throw together in a few months. Which is why all of the credible candidates for the 2028 Democratic nomination (Newsome, Whitmer, Shapiro, etc.) are supporting Biden and will continue to do so, regardless of what happens. It's too late for them to actually build a successful campaign against Trump, and none of them would want to damage their 2028 prospects by losing a race with inadequate preparation and one arm tied behind their back.

Which, again, is why all this speculation about dumping Biden is just fervid imagination. If Biden dropped, the candidate would be Harris - which isn't much of a popularity improvement, given attitudes towards the Administration (not just Biden personally).