I think a lot of what is going on here is bored pundit syndrome. This is the first election in the Internet age where neither party has a competitive primary, so there’s nothing to cover when usually it’s a busy election season. So there has been a lot of manufactured stories about how someone other than Trump or Biden will become a major party candidate when that’s just not going to happen.
I absolutely believe that there is fear and a tinge of regret within the Democratic Party about going forward with Biden, but I think their hands are tied here. As leader of the party, Biden is going to run if he wants to run. The time to replace him as the nominee was November 2022, and Biden wasn’t going to walk away after being one of the few presidents to weather a wave election.
I think Biden probably intended to be a one term president. I think three things changed this:
1: Trump running again. Biden probably went in thinking he would beat Trump and then pass the baton. He (imo wrongly) believes he is the only one who can beat Trump.
2: Harris is less popular than he is.
3: 2022 midterms.
The polling is difficult to read. Obviously Biden is too old to serve. But does that make people vote for Trump? I’m not sure. If a pollster asked me I would tell them that I disapprove of Biden, I think he’s too old, and you better believe I am voting for him in November. The last midterms proved that voters can be more nuanced than polls let on.
Edit: I’ll add the caveat here that if the election were held tomorrow, Trump beats Biden imo. But that speaks more to how volatile everything is. That special counsel report was a Comey level campaign ending bombshell, and we have another 9 months of that to look forward to on both the Trump and Biden side. The biggest one of all is a potential Trump conviction.