Story highlights Bernie Sanders' presidential campaign raised $33 million in the final three months of 2015

Sanders' raised $73 million in 2015

Amherst, Massachusetts (CNN) Bernie Sanders raised $33 million in the final three months of 2015, his campaign said in a statement Saturday, failing to outraise Hillary Clinton but smashing the goal aides set when the Vermont senator launched his campaign back in May.

Sanders' haul -- which brings his 2015 total to $73 million -- was almost exclusively buoyed by his prodigious online fundraising operation. Aides told CNN that Sanders received over 2.5 million donations in 2015 from 1 million different individuals.

Clinton's campaign announced Friday that it raised $37 million for the primary campaign in the last three months of 2015, easily surpassing the $100 million goal the campaign had set earlier in the year.

"This people-powered campaign is revolutionizing American politics," Jeff Weaver, Sanders' campaign manager, said in a statement on Saturday. "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."

The final quarter of 2015 also saw Sanders dramatically increase his spending. According to aides, the campaign ended 2015 with $28.4 million cash on hand. That is only $2 million more than the $26.2 million the campaign had in the bank at the end of the third quarter of 2015, meaning Sanders' operation spent the bulk of what they raised in the fourth quarter.