I remember a curious remark Biden made in an interview (probably during the 2008 campaign, but I forget). The interviewer asked him what he had learned from his years on the Judiciary Committee. Biden answered that he'd learned that ideology matters, and went on to explain that during his early years he thought it most important to pick the most generally qualified candidate and trust them, but later had realized that was wrong: you needed to pick someone who would reliably vote your way. I've long forgotten everything else about the interview, but that remark stuck in my head. If true, it would explain why he would block Posner.