The first play is to split off some of Biden’s African-American support by linking his nostalgia for dealmaking to his less-than-progressive record on race. This is the play Cory Booker is trying to execute, and Booker’s campaign probably depends on its success — which is by no means foreordained, since the African-American vote is more conservative and Biden-friendly than the median white liberal. But nobody before his years as Obama’s V.P. would have regarded Biden as a natural destination for the black vote, and enough sustained tone-deafness in the present could make that past matter once again.
The second play is to make the broader “Uncle Joe” persona, not just its unwoke element, a liability for Biden’s elect-me-to-beat-Trump case. This is probably the Pete Buttigieg play, though it’s available to any younger candidate: Without saying so directly, establish contrasts that make Biden look old, confused, a man out of time, even Trump-y in his own right. Don’t challenge his record, don’t call him a troglodyte — just challenge the conceit that a likable but past-his-prime uncle makes the right contrast with Trump.
The third play is to attack Biden from the center when he flip-flops, and try to break off his more conservative supporters by arguing that the former V.P. isn’t the moderate he used to be.