Bernie Sanders made a very serious run against Hillary in 2016, he was the only big opponent she had. Then, suddenly in the middle of the campaign he just folded and let her run over him in debates, and he just went away. He had had a very good chance to win the nomination.
And the same thing happened again vs Biden in 2020.
There are allegations that in both elections, the Dems bought Bernie off buy buying him an expensive house. Now, Hillary wouldn't do that would she?