What I heard at the time was that only Harris could be handed the campaign stash.
True or not she was the only logical choice, at that late date.
Blame is on everyone who knew Biden was senile. Which is to say everyone. Earlier intervention might have helped. Boo hoo. Live by the brain drained, die by the brain drained.
In the scheme of things, that campaign cash wasn’t a huge deal. It would have been more than made up by the donors that were withholding pledges from Biden.