In the near term, Biden’s achievement indicated that Sanders has no convincing path to defeating this coalition with young people or previous nonvoters. The only formula for his revival would involve Sanders somehow managing to encroach on support Biden won so handily from these groups. If not, it’s shovel time, no matter how long the nomination contest slogs on (which likely will be quite a while).
For the general election, the implications of Tuesday are equally urgent for Trump. Voter turnout in the primaries was up from 2016 in almost every state—in Virginia, for instance, turnout increased by more than two-thirds. The overwhelming evidence is that it is Trump, not any Democrat, who is stimulating this surge. Increased energy on the Democratic side, in the likely event this holds through the fall, means Trump must also stimulate new voters or it is shovel time for him, too.
Perhaps most profoundly, Tuesday night represented history reasserting itself. It was a signal that not all the old ways of thinking about national politics are defunct in an age of disruption.