A big part of the problem was the alternative that we were left with. Both the probable Biden replacement and the near certain aspect of trump winning the republican nomination.
Talk about a rock and a hard place!
Btw, I read this from a different aspect when I looked at it again.
OK, we were left with a bad alternative to Biden......chosen by......Biden.
Let me say this: the choice of VP is - as one commentator put it:
In the Vice-Presidency lies all the potential power of the Presidency itselfâ€â€yet the choice is the most perfunctory and generally the most thoughtless in the entire American political system.
(Theodore H. White, "The Making of the President, 1972," 228).
Biden was not the first Presidential nominee to pick somebody hoping to add or lock down some votes, although the choice of VP matters to virtually nobody. Generally speaking, there aren't enough voters who say "well, I was for McCain, but he chose Palin, so therefore I'm voting for OBAMA."
But Biden was the first one who was going to celebrate his 80th birthday in the White House and should have taken his choice far more seriously as "this person has an above normal chance of becoming President someday." With maybe the exception of Clinton choosing Gore in 1992, almost every single VP choice made by both of the major parties has pretty much ALWAYS been "to lock down or add votes I don't already have." That isn't to say that LBJ, GHW Bush, or Jack Kemp weren't qualified - but let's face it, Agnew/Ferraro/Quayle/Palin most certainly were not.
In the end, "well, we were stuck with a bad choice as our nominee" is a reflection of a failure on the part of the one who selected that person.