Democratic presidential candidate Sen. Bernie Sanders, seen at a campaign event on Dec. 31, raised more than $34.5 million the past quarter, his campaign announced on Thursday. Stephen Maturen | Getty Images

A three-month window that began with a heart attack ended as Vermont Sen. Bernie Sanders' strongest fundraising quarter yet.

Sanders' campaign announced it raised $34.5 million in October, November and December — nearly $10 million more than he had raised in the previous quarter. According to the campaign, $18 million came in from 900,000 individual donations in December alone, as Sanders drew larger and larger crowds to rallies in early voting states such as Iowa and New Hampshire.

Sanders is second to former Vice President Joe Biden in most national polls. The Biden campaign has not yet announced its fourth-quarter fundraising totals. Neither has Massachusetts Sen. Elizabeth Warren, who told supporters in an email several days before the Dec. 31 deadline that she had brought in $17 million and hoped to finish the quarter with $20 million.

Fundraising totals, in millions of dollars, as of 10 a.m. ET on Jan. 2. Third-quarter totals are from Federal Election Commission data. Fourth-quarter totals are reported by the campaigns without providing official FEC filings. Arnie Seipel | NPR/FEC, various presidential campaigns

That would be far less than Sanders, and less than former South Bend, Ind., Mayor Pete Buttigieg, whose campaign announced it raised $24.7 million, an increase of more than $5 million from the previous quarter.

Entrepreneur Andrew Yang also saw a big boost, raising $16.5 million between October and December, compared with fundraising just shy of $10 million in the previous three months.

Yang's ever-increasing fundraising totals reflect his rise from a one-issue candidate to a Democrat drawing sizable crowds, meeting debate requirements and carving out a unique lane in a still-crowded primary field. Meanwhile, President Trump's campaign took in $46 million in the final months of 2019, with more than $100 million in the bank to spend against his eventual Democratic opponent. Trump has consistently outraised individual Democratic candidates, though the Democratic field as a whole has already raised more than Trump in the fourth quarter, based on the fundraising totals announced by just a fraction of the candidates.

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