WASHINGTON — Bernie Sanders’ campaign had less than $6 million at the start of May, a critical cash shortage as he makes an admittedly tough final play to wrest the Democratic presidential nomination from Hillary Clinton.

Sanders’ rival had five times as much money, according to new Federal Election Commission filings, beginning the month with $30 million in the bank.

The two were on roughly equal fundraising footing last month, with Clinton and Sanders each raising more than $25 million. But the Vermont senator spent almost $39 million to Clinton’s $24 million, the reports showed.

This year, Sanders has averaged more than $40 million in spending per month, underlining how quickly he could blow through the cash he had on hand at the beginning of May.

Since he started his presidential bid, Sanders has spent nearly $207 million, about $25 million more than Clinton’s $182 million in expenditures. For her part, Clinton has averaged $26 million in spending per month since January.

Sanders’ heavy campaign spending wasn’t a problem when his online supporters were minting him money. But now that his fundraising has dropped, his high burn rate could hurt his chance to continue competing.

Even as he racked up primary victories last month and sharpened his attacks against the former secretary of state, online donors started holding back. Sanders raised considerably less in April than his record-setting $46 million in March or $43.5 million in February.

The Sanders campaign began taking steps late last month to downsize its operation. He reduced his payroll from about 1,000 to fewer than 400 employees. Sanders has pledged to continue in the race until the final primary, June 14 in Washington, D.C.

The latest reports showed that Sanders spent about $21 million on media buys and digital consulting. The campaign paid $17.3 million to Old Towne Media Inc., based in Alexandria, Virginia, and more than $3.6 million to Revolution Messaging, a Washington advertising firm that concentrates on digital outreach.

Sanders plans to spend a little more than $525,000 on television and radio advertising in California ahead of its June 7 primary, according to advertising tracker Kantar Media’s CMAG. Clinton has not reserved any airtime there.

Clinton has tended to spend less on ads than Sanders. In April, her campaign spent about $9.3 million on media buys and $2.7 million more on online advertising, her report showed.

Sanders reported raising $26.9 million in April through his campaign. Unlike Sanders, Clinton has been fundraising for months in partnership with the Democratic National Committee and state parties. Through that joint fundraising account and her campaign, she raised $26.4 million in April for her primary battle with Sanders, though fundraising expenses sliced off about $1.4 million.

Meanwhile, the DNC and state parties that have benefited from Clinton’s fundraising help have begun investing in likely general election battleground states such as Ohio and Florida.