But to call that a long-shot hope might be an overstatement. Before the Wisconsin primary come Arizona, Florida, Illinois, Ohio and Georgia, all diverse states where Mr. Biden will most likely claim victory.
According to an analysis by my colleague Nate Cohn, Mr. Sanders would need to beat Mr. Biden by about eight percentage points in the remaining contests to capture the nomination. Given his position in the polls, that means improving his standing by about a net 30 percentage points — a herculean task.
So, why not just drop out of the race today?
Part of the reason is that Mr. Sanders sees himself as leading not just a campaign but a movement. His policy positions, on issues like free college and “Medicare for all,” are broadly popular, and his presidential bids have shifted the center of gravity within the party to the left. Staying in the race gives Mr. Sanders perhaps his highest-profile moment yet to pull the party and Mr. Biden further in his direction.
Unlike many of his competitors (ahem, Elizabeth Warren, Pete Buttigieg, Amy Klobuchar, Cory Booker, Kamala Harris, even Andrew Yang), Mr. Sanders is unlikely to be able to mount another campaign — both because of his age, 78, and the fact that he will have run twice already. So there’s less of a personal imperative to leave the race early to preserve future political prospects.
Aides also say Mr. Sanders disdains President Trump and, above all, wants to see the president defeated.
Mr. Sanders knows that Mr. Biden cannot win the general election without the backing of his supporters. By staying in the race, Mr. Sanders can prepare them for his exit and give Mr. Biden — not yet the presumptive nominee but inching closer — a chance to make overtures.
We started to see that last night, when Mr. Biden used his remarks after polls closed to welcome Mr. Sanders’s supporters into his camp.