Comment by danaris

Biden was by far the most effective and most progressive Democratic president of the post-WWII era.

What "hammered home" the disillusionment was not Biden's actions*, but rather the media narrative built around him, particularly by the newspaper most identified with the Democratic Party: the New York Times. They were angry that he didn't give them deference early on, and that, combined with the desire of their wealthy Republican owner to push his politics, led to the constant drumbeat of stories about Biden's supposed "cognitive decline", when he's still much sharper than Trump.

ETA: ...not to mention totally ignoring all his very real accomplishments, like forgiving the student debt of millions of people (yes, despite not getting as many as he wanted, he really did achieve that) and the infrastructure bill.

* His inaction, particularly on prosecuting Trump, was a separate matter.