Depends a bit on whether the Orange Man runs again, since Joe's whole raison d'etre was to be a caretaker after Hurricane Donald. And it depends a lot on how well they can reverse/arrest/conceal his cognitive decline.
Harris is clearly out of her depth and she knows it; hence her obvious nervousness. Let's remember, she got lots of glowing press, and then did not even make it to Iowa. The fact that her staff is bailing despite her being the heir apparent tells us quite a bit.
Mayor Transportation Secretary Pete? His first shot at the national stage during the shipping and trucking supply chain crisis and he's at home with his husband and their two adopted infants for paternity (is that a word anymore?) leave.
How about the other Geezers? Jay Inslee's north of 70 and ran in 2020, although fortunately probably nobody remembers it. Folks do probably remember Elizabeth Warren's run, but not for good reasons. She finished third in her own state.
The Democrats tend to fall in love with someone relatively new. If Stacey Abrams manages to pull off the win in Georgia, she would be well-positioned. Arguably the same applies to Beto in Texas, although the way he fizzled out after all the publicity ("I was born for this,") puts him in the same class as Harris, and Texas is going to be a lot harder row to hoe.
AOC? Something of a wildcard at this point. Bernie is still in that lane, but she would be well-positioned if she gets his endorsement. She'd barely be eligible (she'll turn 35 two weeks before election day), and might prefer to wait another cycle or two.