First Feinstein... Her resigning is such a no brainer. She comes from a very liberal state and a replacement will be very liberal. I think they are hoping this problem will limp into 2024 when she can retire. Ronald Reagan comes to mind in the last couple of years of his term.
I think Biden will do the same thing. Win the election and slowly back off and eventually let Harris take over. I know how much you hate Harris but Biden could hold on as long as possible. A good president delegates a lot of responsibility out to his minions. I don't see this as a huge problem. Sure, I don't want him to run again, but time is running out and Biden winning big could put a stake in the heart of the MAGA cult (so much winning!)