The 74-year-old junior United States senator from Vermont lost four of Tuesday's five major primaries to former secretary of state Hillary Clinton, making it virtually impossible for him to win the Democratic nomination.
Sanders now plans to cut hundreds of staffers, his campaign spokesman Michael Briggs confirms to PEOPLE.
"We've gone from a peak of more than 1,000 in January before the Iowa caucuses and New Hampshire primary to about 325 to 350," Briggs explains. "We're 80 percent of the way through the primary and caucus calendar and this right-sizing of the campaign staff will leave us with the people we need for a strong finish in California and the other remaining states and territories and the District of Columbia."
Briggs adds, "Our fundraising remains strong. We owe it to the people who have made 7.3 million donations averaging $27 apiece to marshal our resources and spend them wisely and efficiently."
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Sanders trails behind Clinton by more than 200 pledged delegates going into the 14 remaining Democratic primaries – including California's on June 7 and next week's in Indiana.
Ahead of Tuesday's primaries, Sanders sent an email to his supporters promising to "fight the narrow path we have to the nomination," according to the Washington Post, and said he'd stay in the race until the summer convention.
On Wednesday, the Brooklyn native said of the campaign cuts and Clinton's victories, "what we are going to do is allocate our resources to the 14 contests that remain, and that means that we are going to be cutting back on staff," according to the New York Times.
He added, "We have had a very large staff, which was designed to deal with 50 states in this country; 40 of the states are now behind us. So we have had a great staff, great people."