A handful of Democratic presidential candidates are touting the amount of money they've raised in the first fundraising period of a 2020 primary fight that will last into next spring. The totals for the first quarter, which ran through March 31, are the first measure of how candidates are faring.

Details for the entire field won't be known until candidates file their required disclosures with the Federal Election Commission by April 15, but here are some takeaways from what the campaigns have released so far:

BERNIE REALLY IS A FRONT-RUNNER

Bernie Sanders joins former Vice President Joe Biden atop many polls of prospective Democratic primary voters. But Sanders has something Biden doesn't have (yet): a campaign operation raking in cash.

The senator from Vermont, who showed surprising fundraising heft in his upstart challenge to Democratic presidential nominee Hillary Clinton four years ago, raised more than $18 million in the 41 days between his official campaign launch and March 31, giving him $28 million cash on hand.

Those totals are expected to lead the Democratic field, putting pressure on other heavyweights, including Biden, who is still deciding whether to run and who is navigating accusations that he's acted inappropriately toward women.

Besides Sanders, Sen. Kamala Harris of California put up an impressive $12 million haul. Former U.S. Rep. Beto O'Rourke of Texas reported $9.4 million, a noteworthy sum given that it came in 18 days.

Sanders' haul shows that his base is just as enthusiastic as it was four years ago. In fact, it may be growing. The senator's campaign noted that of his 525,000 unique donors, about 20% are new, about 100,000 are registered independents and about 20,000 are registered Republicans.

As impressive as Sanders' fundraising has been, it's not as large as previous presidential contenders who were more reliant on big donors.

In her first quarter as a candidate ahead of 2016, Clinton topped $45 million. In 2007, when then-Sen. Barack Obama and Clinton were beginning their long battle for the 2008 nomination, the favored Clinton opened with an initial fundraising quarter of $36 million, while the underdog Obama pulled in $26 million.

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EXPECTATIONS GAME: MAYOR PETE WINS

Sanders' fundraising haul set the curve for all candidates and will give pause to some of the other perceived heavyweights in the field, particularly his fellow senators Harris, Amy Klobuchar of Minnesota, Cory Booker of New Jersey, Kirsten Gillibrand of New York and Elizabeth Warren of Massachusetts. (Harris is the only candidate of that group to release her fundraising totals.)

But the biggest winner may be Pete Buttigieg, an unlikely headline-grabber even among a group of lesser-known candidates that includes governors and members of Congress.

The 37-year-old mayor of South Bend, Indiana, raised $7 million, calling it "a great look for our first quarter." That might be an understatement.

Such a sum ensures Buttigieg can finance a legitimate campaign operation for months as long as he's not a profligate spender. (Former Wisconsin Gov. Scott Walker learned in the 2015-16 Republican presidential campaign that being an early fundraising leader is no guarantee of success; he spent big, ran out of money and dropped out before the Iowa caucuses.)

Just as important as the bottom line: Buttigieg said he has almost 160,000 unique donors, a mark that meets the new grassroots fundraising threshold that the Democratic National Committee has set for candidates to qualify for the initial summer debates.

O'Rourke's number also is impressive, and his campaign emphasized that his nearly $10 million came in just 18 days. But that doesn't mean he can sustain that per-day clip. Sanders, for example, raised $10 million (more than half his total) in his first week.

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SMALL DONORS RULE THE DAY

It's a new day in Democratic politics, with small donors carrying the day.

Sanders touts that he's held zero traditional fundraisers and has an average donation of $20 — less than 1% of the $2,800 maximum. Sanders' campaign says the senator got 88% of his money from donors who contributed $200 or less.

Buttigieg said his average contribution is about $36, with 64% of his total coming from those donating $200 or less. Andrew Yang, an entrepreneur who's never held political office, has raised just $1.7 million, but his campaign says it's come from about 80,000 donors averaging less than $18 per contribution.

O'Rourke said his average contribution was $43, with 98% of his donations coming from people giving less than $200.

This shift largely reflects politicians reacting to a progressive base that looks with suspicion and distrust on big-money donors.

For example, Warren is among the perceived favorites in the field but has promised she'll be financing her campaign without leaning on traditional donors.

Harris isn't eschewing high-dollar fundraisers. In a recent stop in Atlanta, she held one small-dollar event but also a high-dollar gathering sponsored by bundlers who'd pulled together at least $28,000 for her campaign. Yet when her campaign aides released fundraising totals for the first quarter, it wasn't the big checks they touted. Rather, they emphasized that 98% of her contributors gave less than $100.

Gordon Giffin, a former Canadian ambassador under President Bill Clinton, recently hosted a fundraiser for Klobuchar in his metro Atlanta home. Traditional fundraising isn't going away, Giffin said in a recent interview, "but that grassroots money can more than make up for it, and candidates have to prove they can do that."