What can be derived from all this is that almost none of what made Joe Biden attractive to Barack Obama as a vice president in 2008 is likely to prove helpful to the candidate in 2020, and that much of it is likely to prove encumbering to him. He is the designated white guy in a party that does not want one this time around or believe itself to need one. And three cheers for that: Joe Biden’s political redundancy might, from this point of view, be welcomed as a kind of milestone in American racial politics, not quite so significant as Barack Obama’s election to the presidency but certainly complementary to it.

Barack Obama is, as of this writing, maintaining an absolutely prudent and practically monastic silence on the 2020 Democratic primary. If he had been so circumspect as president — if he had had just a slight touch of Calvin Coolidge upon his soul — he might have become the great unifier that had been so intensely hoped for by many of his admirers and more than a few of his critics. But he was what he was, and his presidency’s main bequests to the country are an even more deformed body of health-insurance regulations and a heightened feeling of whatever product you get when you multiply cynicism by paranoia.

Whatever we do, let us please abandon the notion of Joe Biden as an avuncular, conciliatory, reasonable politician of the courtly old school. Whatever his contribution to Obama’s presidency, Biden’s legacy already is fixed and has been since long before anybody cared about that stirring young state senator from Illinois: Joe Biden will be remembered for his central role in the Robert Bork and Clarence Thomas hearings, during which he arguably did more than any other living American to convert ordinary partisanship into scorched-earth culture war. Dopey old “Uncle Joe”? He is as vicious and conniving a man as the politics of our time has thrown up. But even his viciousness will not save him in 2020. In that, the teacher has been surpassed by his students. If they tear him apart, as I expect them to, there will be some poetic justice in the spectacle.