Bernie Sanders's well-oiled fundraising machine is showing no signs of slowing down.

For the second straight month, Sanders relied on small donors to outraise Hillary Clinton, raking in $14 million more in February, according to numbers released on Sunday by the Federal Election Commission.

Sanders has now received $77 million from those giving less than $200, while Clinton has received $32 million from the same category, data from the Campaign Finance Institute shows.

Sanders's strength with these kinds of donors has been clear for months. But most campaign finance experts say they have been awed by the durability of his fundraising prowess: Sanders has now received more in small contributions than even Barack Obama had at this point in 2008, according to Michael J. Malbin, executive director of the Campaign Finance Institute.

Bernie Sanders's March FEC report is 188,613 pages long. Damn. — Reid Wilson (@ConsultReid) March 21, 2016

Clinton has drawn the vast sum of her money from people giving the maximum of $2,700. But whereas those donors are prohibited from giving more to her this primary cycle, Sanders can return again and again to most of the 5 million people who have filled his coffers.

"This money is just bubbling up from everywhere," says Bob Biersack, a senior fellow at the Center for Responsive Politics, "and there's nothing that would cause it to stop."

What Sanders's fundraising haul means for the primary

In the short term, Sanders's fundraising haul means he'll have enough money in the bank to sustain a primary challenge against Clinton all the way to the Democratic National Convention, regardless of how far behind he is in the delegate count.

"You have to have enough funding to continue to be a visible campaign, with people and staff on the ground," Biersack said. "Sanders raised an incredible amount in February. He will have enough resources."

That's going to be particularly important for Sanders's search for delegates in bigger states, like Pennsylvania and New York, where it will be crucial to have well-staffed ground games, according to Biersack.

Of course, the Vermont senator remains an underdog in the race overall. And while he raised more money in February than Clinton, he also spent more — $40 million to Clinton's $34 million, according to the Washington Post.

Still, Sanders has done best in states where he's had time to get his message out.

In Michigan, for instance, he outspent Clinton $1.2 million to $979,000 on TV ads, airing 675 more segments than she did on his way to an upset victory. Sanders's donors have ensured that he'll be able to fill the airwaves for months to come.

The difference between Clinton and Sanders's fundraising strategies

Sanders's model represents a break from what political consultants consider the traditional way of fundraising: Compile a Rolodex of wealthy donors, then tap them and their friends for the maximum $2,700 contribution.

"That's the way national campaigns usually go," Biersack said.

Clinton has largely relied on this basic formula. Of the $107 million her campaign has raised, about 51 percent of her donations have come from those giving the maximum contribution compared to 3 percent of Sanders's, according to the Campaign Finance Institute. (Clinton backers have formed one major Super PACs — the fundraising committees with no limits on donations — but it hasn't spent any money in the Democratic primary.)

It's not that Clinton has failed to fundraise among those giving in small amounts.

In February, she pulled in $10.5 million in minor contributions — by far the most of any candidate in the field except Sanders. And her use of "bundlers" for cash is hardly unusual, even among Democrats: Obama, for instance, drew heavily on them to roll together big checks from the rich.

Still, Sanders's campaign has a point when it says Clinton is much more dependent on wealthy donors.

Clinton's website has a whole page, "Hillblazers," thanking the 354 elite donors — including lobbyists and Wall Street bankers — who have helped her raise $100,000 or more. Overall, Clinton has taken in a whopping $79 million from those maxing out their donations.

Portion of campaign cash from donors giving legal max of $2,700:



Clinton: 51%

Sanders: 3%https://t.co/h5VPdVXP1H h/t @cfinst_org — Michael Beckel (@mjbeckel) March 22, 2016

Can Sanders's fundraising juggernaut be replicated by future Democratic candidates?

Clinton's dependence on mostly wealthy individual donors has gotten her plenty of money. But it's also gotten her campaign in political trouble.

Consider the following controversies she's had to deal with related to her fundraising:

She's been under repeated attack for giving three speeches to Goldman Sachs in exchange for $675,000.

She's been criticized for using dozens of elite lobbyists to package donations for her run.

Just last week, Clinton came under heavy fire when news surfaced that the CEO of Theranos, a health care firm criticized for misleading the public about its blood testing technology, would be hosting a fundraiser headlined by Chelsea Clinton. (The event was later canceled.)

There's also evidence from the right this year that traditional fundraising is a political liability: Donald Trump, the Republican frontrunner, has made his relative independence from wealthy backers a key part of his campaign pitch.

The campaign finance experts stress that it's important not to overstate how much Sanders's success will change the rules of the game.

Malbin, for instance, notes that Sanders is waging an unusual campaign where his message — that money has corrupted America's political system — also matches his call to give. And there's no guarantee that what he's done can be translated into a congressional or gubernatorial race, or even another presidential one.

But Sanders has at least proven that there are the dollars and the contributors to power a national presidential campaign essentially through small donors alone.

"There is really another way," Biersack said. "The challenge is to figure out how to strike the match."

Bernie Sanders on campaign finances