Sen. Elizabeth Warren (Mass.), a Democratic presidential candidate, speaks at the National Action Network convention in New York on April 5. (Seth Wenig/AP)

Sen. Elizabeth Warren’s presidential campaign raised $6 million during the first quarter of 2019, a haul that puts the onetime financial juggernaut behind several of her rivals in the Democratic nominating contest.

“I won’t sugarcoat it,” Roger Lau, her campaign manager, wrote in an email to supporters on Wednesday afternoon. “We were outraised by some other candidates in the presidential primary this first quarter. You might have seen some of the big numbers in the headlines, from $7 million to $18 million.”

Warren was the first major candidate in the race, with a vaunted email fundraising list that she used to build a small-donor network that helped her finance her U.S. Senate campaigns in Massachusetts and that also allowed her to raise money for other candidates across the country.

In the first quarter, Warren raised funds from 135,000 donors who made more than 213,000 donations, a level that her campaign says will allow her to be competitive. She raised more than $1.4 million during the final week of the first quarter, leading her staff to say some momentum had developed after a more dismal start. Sen. Kamala D. Harris (Calif.), by comparison, reported raising $1.1 million during the final week.

But overall, other candidates dwarfed Warren’s campaign in the first quarter of the race.

Sen. Bernie Sanders (I-Vt.) raised $18.2 million from 525,000 people, while Harris brought in $12 million from 138,000 donors. Warren also trailed South Bend, Ind., Mayor Pete Buttigieg, who brought in $7 million from nearly 159,000 donors after a recent surge of interest.

The issues 2020 Democrats are running on, according to their social media

Former congressman Beto O’Rourke (Tex.) raised $9.4 million from 163,000 donors, with the bulk coming during his first 24 hours as a candidate; he raised more in that day than Warren did during the entire three months.

Warren only narrowly outraised the $5.2 million reported by Sen. Amy Klobuchar (Minn.) and the $5 million reported by Sen. Cory Booker (N.J.). Both entered the race more than a month after Warren, who announced her candidacy on New Year’s Eve.

Warren aides said the campaign raised more money than it spent, but the margins appear narrow. She transferred $10.4 million from her U.S. Senate account, and the cash on hand was about $11 million at the end of the quarter, a campaign aide said.

Warren has built one of the largest campaign operations so far, with more than 170 staffers now, about half of them in the four earliest-voting states.

But Warren made a calculated gamble weeks ago to eschew large donor events, hoping that her ability to differentiate herself from candidates such as Harris and run an overtly grass-roots campaign would offset the loss of income.

In some ways, the fundraising report illustrated the downside of relying only on small donors. Warren’s campaign said the average donation was $28, the same as it was for Harris’s online donors. But because Harris also did larger fundraisers, she brought in more money for an overall average donation of $55.

“Elizabeth decided not to do any closed-door events with wealthy donors, or call time where candidates typically call wealthy people and personally ask them to donate,” Lau wrote in his message to supporters. “Ninety-nine percent of our donations were $200 or less. That isn’t a coincidence: that was by design.

“We don’t have to match other candidates dollar for dollar, but we do need a strong enough grass-roots base to be able to keep Elizabeth’s voice front and center in this race,” Lau added.

Warren earlier on Wednesday released her 2018 tax return, which showed more than $900,000 in family income. The move made her the latest presidential candidate to provide their most recent personal finance information as Democratic rivals pressure one another to be more transparent and counter President Trump’s unwillingness to release any of his tax documents.

Warren’s release of her tax return followed that of several other candidates — including Sen. Kirsten Gillibrand (N.Y.), Klobuchar and Washington Gov. Jay Inslee — and came a day after Sanders promised to release his returns by Monday.

In August, Warren released 10 years of her tax returns, a period that covers her tenure representing Massachusetts in the Senate and earlier government service. She has filed legislation that would require the Internal Revenue Service to release the tax returns of presidential and vice-presidential candidates for the previous eight years, as well as during each year in federal elective office.

“There’s a crisis of faith in government — and that’s because the American people think the government works for the wealthy and well-connected, not for them,” Warren said in a statement. “And they’re right. I’ve put out eleven years of my tax returns because no one should ever have to guess who their elected officials are working for. Doing this should be law.”

According to her returns, Warren and her husband, Bruce Mann, reported earning $905,742 in total income, including $176,280 from her Senate salary and $324,687 from her books. She and Mann, a Harvard Law School professor, paid $230,965 in taxes. They reported donating $50,138 to charity.

Sanders pledged in February to release 10 years of tax returns, and several times has said they would come out “soon.” On Tuesday, he said they would be released by April 15 and would reveal that he is a millionaire, which he attributed to income from a book deal.

O’Rourke, who entered the presidential contest in March, has said that he plans to release his tax returns but has not said when.

Former vice president Joe Biden, who is likely to enter the race later this month, has released 18 years of tax returns covering a period up to 2015. He has not committed to releasing additional returns.