I think if they conclude secretly that Trump can’t be beaten in 2020 they will go full retard with Kamala Harris and try to pave the way for a return to a “stereotypical folksy sober white male moderate governor” as their candidate in 2024.
I agree with your sentiment, that the 2020 Dem candidate will be a sacrificial lamb for the party. That's why I think Beto and Kamala will run, for the experience, but the winning Dem candidate will be Slow Joe.
He'll end his political career with a humiliating double-digit drubbing while the DNC power brokers secretly snicker behind his back. He'll never see it coming...