Warren and Sanders, who raised $25.3 million, both finished about $10 million ahead of former Vice President Joe Biden for the quarter.

Biden, meanwhile, fell back in his fundraising, posting $15.2 million – about $7 million less than he raised the previous three months. And other Democrats who relied on traditional, big-dollar fundraisers also slipped, presaging difficulties financing robust campaigns.

Sen. Kamala Harris’ reported haul of $11.6 million came in slightly lower than her second quarter. And though South Bend Ind., Mayor Pete Buttigieg posted $19.1 million, that number was down, too, from the previous three months, when he raised $24.8 million.

“The fact that progressives combined to raise $50 million without one fundraiser is mind-boggling,” said Rebecca Katz, a progressive consultant who advised Cynthia Nixon in her primary campaign against New York Gov. Andrew Cuomo last year. “And really exciting, because they showed there’s a better way to do this.”

The quarterly fundraising reports marked a victory for the progressive wing of the Democratic Party. And its effects were felt more broadly than on the candidates’ bottom lines. Freed from the time constraints of traditional fundraising, Warren spent hours in photograph lines at campaign events throughout the summer, while Sanders — before his hospitalization this week — maintained a frenetic pace on the trail.

And as the campaign accelerates this fall, Warren and Sanders are poised to compound the effect of their small donors. Unlike contributors who give the maximum amount at exclusive donor events, small-dollar contributors can re-up repeatedly.

“Anybody whose core model is big-money fundraisers will get tapped out at some point and have diminishing returns,” said Adam Green, co-founder of the Progressive Change Campaign Committee, which has endorsed Warren, “whereas 10- and 20-dollar donors can keep coming back to the table over and over again.”

Biden, the longtime frontrunner, still leads Warren and Sanders in many national polls. The latest Morning Consult survey put him at 32 percent, with Warren and Sanders at 21 percent and 19 percent, respectively.

William Owen, a Democratic National Committee member from Tennessee who has endorsed Biden, said that despite “a huge amount of money” for both Sanders and Warren, “Joe is still in the lead with the voters.”

And the flurry of financial reports suggested an opening at the periphery of the top tier for other candidates. Sen. Cory Booker raised more than $6 million in the third quarter amid a surge of support in late September. Businessman Andrew Yang raised $10 million. And Harris’ campaign said it has nearly that much on hand.

“This is where the campaign season, I think, takes on a different kind of urgency,” Buttigieg said when he arrived at a gun control forum in Las Vegas this week. “Something about fall, I think, brings a certain focus to it.”

Voters, Buttigieg said, are “really getting into decision mode.”

Lesser-fundraising candidates – and many observers – can recount a litany of well-funded candidates who have failed before in presidential elections. And Matt Bennett of the center-left group Third Way, said Friday that the 2020 primary may require less money than most elections.

“In a primary like this one where the frontrunners have pretty significant name ID,” he said, “they don’t need to introduce themselves to voters.”

Biden, Warren and Sanders will all have enough money to fund robust field operations, he said, and “beyond that, the marginal difference between $25 million and $15 million, I think, is relatively small.”

“I do think the money matters in the second tier, but it matters less at the top tier,” he said.

In addition, online fundraising can fluctuate wildly. While Warren’s ascent has proved relatively steady – what Gretchen Dahlkemper, a Democratic strategist based in Philadelphia, described as “like a duck … kicking underneath and keeping calm” — other candidates who have relied on small donations have faltered.

Beto O’Rourke, who has not yet announced his third-quarter fundraising, raised more than $80 million in his near-miss Texas Senate run last year and followed that with $6.1 million in the 24 hours after he announced his presidential campaign in March. But by July, O'Rourke — who like many candidates relies on a mix of online and traditional fundraisers — reported a dismal $3.6 million in the second quarter.

Les Francis, a Democratic strategist and former deputy White House chief of staff in the Carter administration, said it is an open question “whether or not there’s a ceiling to that progressive donor base. In other words, does it get exhausted at some point? And, I don’t know the answer to that. We’ll find out.”

However, he said, for centrists, Biden’s figures are “troubling when you combine it with the numbers of the other so-called moderates in the race.”

“By definition, moderates are hard to get excited,” Francis said. “That reveals itself not only in fundraising, but in volunteer activity and all the rest.”