First, Mr. Biden has diminished his appeal as a challenger to Mr. Trump with subpar live performances, including frequent stumbles on the campaign trail and low energy on the debate stage. Major donors have hedged their bets, and pundits are questioning how he will ever go toe to toe with Donald Trump if he can’t handle Kamala Harris.

Second, there has been a significant shift in how the money game works. Attracting a massive number of small donors is now more important than megadonor-driven political-action committees. And Mr. Biden so far has been a terrible small-dollar candidate. After initial success when he announced, his online numbers have nose-dived. This trend will keep up as his claim that he is the best candidate to beat Mr. Trump continues to evaporate.

Finally, there is going to be a dramatic reset of the table after candidates begin dropping out. Most of the candidates departing will be to the left of Mr. Biden, and their supporters will likely gravitate toward more prominent left-wing candidates. Eventually they may coalesce around one viable populist-progressive candidate, giving Democrats an obvious option for a brash challenger to Mr. Trump.