I'm expecting a Harris vs. Warren primary. It probably inevitable that there will be a progressive challenger and Warren seems to want to run again.
I have to imagine that, in a one-on-one contest between VP Harris & Warren, Harris would win the nomination by just replicating Biden's 2020 primary numbers in the South, managing to get a decent home-state advantage in CA, & winning maybe 1 or 2 other states with decently-sized Black populations (e.g., NY). Warren could literally win the rest of the country (e.g., the entire Midwest, everything in the West except CA, & most of the Northeast), but Harris wins the nomination because she wins her states by much bigger margins. I think Harris would still win even with a map like this:
Vice President Kamala Harris (D-CA)Senator Elizabeth Warren (D-MA)