It is ironic, I suppose, that such a large and diverse pool of candidates should dwindle to two old white guys. For some identity-oriented Democrats, it is worse than that–it is a tragedy. Should they be so concerned?
My advice is to be patient, because things will be very different in 2024. Sanders will be too old to run then. If Biden wins in 2020, it is unlikely that he will choose to run for re-election, and we already know he will have a female VP. If he loses, he will be out of the picture in any event, and the field will be clear for Harris, Klobuchar, Booker, et. al.
And, of course, AOC will be eligible to run by then. She has a good chance of being the nominee if we have to suffer through a second Trump term.