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Senator Bernie Sanders of Vermont raised just $25.8 million for his campaign in April, down by more than 40 percent from the previous month, as he faces an increasingly narrow path in the race for the Democratic nomination for president.

The April total, released by his campaign on Sunday, brought Mr. Sanders’s cumulative fund-raising haul to $210 million from more than 2.4 million donors.

He raised almost $46 million in March, his best month yet in a contest during which he has frequently brought in more money than his Democratic rival, Hillary Clinton.

Earlier this week, Mr. Sanders revealed in an interview that he would be laying off some 255 workers, saying he would focus his resources on competing in the remaining 14 contests, particularly in California.

Mr. Sanders has faced questions about how much he can continue to raise as Mrs. Clinton has pulled farther ahead in the competition for Democratic delegates. But he is continuing to bring in large sums of money from donors making small gifts: 540,000 people contributed in April, the campaign said.

“What our campaign is doing is bringing millions of Americans into the political process,” his campaign manager, Jeff Weaver, said in a statement. Four in 10 contributors are between 18 and 39 years old and the most common professions of donors are teachers, students and engineers, the statement said.

Seeking to minimize the drop in fund-raising, the campaign’s spokesman, Michael Briggs, stressed that Mr. Sanders’s average monthly fund-raising total was only $17 million. But that factors in Mr. Sanders’s fund-raising going back a full year to the start of his campaign.