I don't think it was strictly sexism and racism that led to their failure. Clinton was an elitist insider who arrogantly thought the presidency was "her turn" as part of a political dynasty while working with the DNC and the other establishment candidates to sabotage Sanders' campaign. I was pissed learning of her leaked emails collaborating with DNC administrators to thwart Sanders every step of the way.

Harris was a milquetoast politician who was basically appointed to be the Democrat candidate when Biden announced he wouldn't run for a second term long after the primaries could have been held. Could she have done a better job had she distanced herself from Biden's foreign policies? Possibly, but she held firm to the status quo which was not gonna fly with a lot of those who knew the horrors Israel was inflicting on Palestinian civilians.

A lot of us on the left have this notion that our candidate has to be near perfect to win their vote and that also tends to hurt their chances. Couple that with the DNC getting high on its own neoliberal farts and you tend to get a losing combination.

AOC doesn't have the same kind of baggage that made both Clinton and Harris undesirable to many so there's a better chance she could make it, especially with the way Trump has ratfucked the US and the world at large. Her championing Sanders' policies will also be a big boost to those who want a more affordable and equitable life too.