Sanders, an independent and a democratic socialist, has now collected $73 million for his primary campaign through a powerful online fundraising apparatus that should help him compete with Clinton deep into spring. His haul will allow him to spend money at a comparable rate with Clinton, who raised $37 million since the beginning of October and $112 million during 2015 for her primary campaign.
"This people-powered campaign is revolutionizing American politics," Jeff Weaver, Sanders' campaign manager, said in a statement. "What we are showing is that we can run a strong, national campaign without a super PAC and without depending on millionaires and billionaires for their support. We are making history, and we are proud of it."
Clinton is the Democratic front-runner in national polls, but Sanders remains within striking distance of her in Iowa, which holds its caucuses on Feb. 1. Sanders is hoping to surprise Clinton in Iowa and then use his New England ties to defeat her in the New Hampshire primary on Feb. 9, where polls have shown him with a slight advantage.
The campaign finance estimates indicate that Sanders should have the resources to mount an effective challenge: His campaign said it had $28.4 million in the bank at the end of 2015.
Clinton's campaign, which spent about $75 million last year to build a large data-driven organization, ended the year with $38 million on hand. Sanders spent about $45 million in 2015. He stepped up his expenditures during the fourth quarter, when he began television advertising and increased the size of his paid staff in early-voting states.
Most of Sanders' money came through 2.5 million donations, most of them made online, a number that his team said surpassed President Obama's record number of 2.2 million donations in 2011.
Sanders' average donation was $27, an amount that will allow him to return to his contributors for more money in the spring. Only a few hundred of his 1 million individual donors gave the maximum of $2,700 for the primary, the campaign said.
But Clinton is also helping build the Democratic Party for the general election. She raised $18 million for the Democratic National Committee and state Democratic parties nationwide in the fourth quarter, putting her total haul for the last three months at $55 million. The DNC money is aimed at helping Clinton in the general election should she win the party's nomination.
Sanders, by comparison, did not raise any money for the DNC last year, although his campaign has said it plans to fundraise on behalf of the national party.