I just don't see what most are seeing in Biden. On paper he's the candidate closest to the center and would probably have an easier time winning over the three states Trump took by 80,000 or so votes in 2016, but how is he going to excite the base and survive the grueling grind of the general election campaign against Trump? The mere fact that he's an old, white man means he's swimming against the "blue wave" ushered in by women in 2018. The Dems used women to protest against Trump and to attempt derailing Kavanaugh, too - it's been what I thought has been an obvious strategy to increase the likelihood of the first woman president. Pelosi also used her gender to secure her position as House Speaker.
I thought that Biden looked like he was teetering on the edge of collapse at points during his CNN debate when he got worked up. Replacing the one time use of "my time's up" at MSNBC's debate with several uses of "anyway" didn't exactly demonstrate strength either. He's pitched himself as a fighter that would take Trump out behind the gym, but did anyone see that from him this past week?
I don't think Harris is anymore done than Biden was after MSNBC's debate. If she drops out the California primary changes drastically.