Michigan was the signature win of his 2016 bid. Four years ago, he won more than 70 percent of the vote in caucuses in Washington and Idaho. Yet Mr. Sanders is not clearly favored to win Washington at this hour and lost Idaho, and his loss in Michigan carried even more weight because of his strength there four years ago.

The difference between winning and losing is not particularly relevant from a delegate standpoint. It is highly relevant for momentum: Victories bestow positive news coverage. A string of victories is one of the few ways that Mr. Sanders might hope to build momentum and change the course of the race, as he did in Michigan four years ago and as Mr. Biden recently did in South Carolina.

If Mr. Sanders is not clearly favored to win in Washington and lost Idaho, he’s probably not favored to win anywhere. There are a handful of primary states that might be just as close as Washington — like Oregon or Montana or Rhode Island — but few ought to be much more favorable to Mr. Sanders.

He prevailed in North Dakota, but the race was a so-called firehouse caucus — a party-run primary where voters cast traditional ballots at a small number of locations statewide. Support there for Mr. Sanders might not suggest success beyond the other small states with party-run primaries or caucuses: Alaska, Hawaii, Kansas and Wyoming. Indeed, he fared poorly along the Minnesota side of the border with North Dakota in the Minnesota primary on Super Tuesday.

At this point, Mr. Sanders has one realistic way to change the course of the race before next Tuesday’s contests: the debate on Sunday. But by then, millions of voters will have cast early ballots in Florida, Arizona and Ohio. It would be too late to completely alter the outcome, much as Mr. Biden was unable to fully capitalize on his surge in the Western states because of significant early voting before Super Tuesday.