Bernie Sanders burns through $50 million in last three months of the year

The Vermont senator started January with $18.2 million remaining in his bank account to face a slew of early state contests, according to his campaign filings with the Federal Election Commission. Around the corner: 14 Super Tuesday states in early March and with them wildly expensive advertising markets in places like California.

But Sanders and former Vice President Joe Biden remain atop the Democratic field in national polling, and a win or strong finish for the Vermont senator in Monday's Iowa caucuses could provide the momentum and fresh donor support to replenish his funds. His campaign already has touted strong fundraising performance in January, saying it raised $1.7 million during the nationally televised primary debate in mid-January.

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Sanders also has relied on a strong base on small-dollar online donors -- who can be tapped repeatedly for donations before they hit the $2,800-contribution limit -- to fuel his campaign. Small-dollar donations accounted more a little more than half of the contributions Sanders received during the final three months of the year, the filings show.

His campaign is looking ahead to Super Tuesday and recently bought $2.5 million worth of ads in delegate-rich California and Texas.

Friday is the deadline for campaigns to disclose the end-of-the-year fundraising and spending. As of late Friday afternoon, only two other Democratic candidates, had filed fundraising reports: billionaire Michael Bloomberg, who reported plowing $200 million of his own money into the campaign at the end of last year, and Colorado Sen. Michael Bennet, who trails in the polls. Bennet reported having about $517,000 remaining in his campaign account.