WASHINGTON — Democratic primary front-runner Joe Biden reported on Wednesday that he raised $21.5 million since launching his White House bid, a sum that has the former vice president trailing Pete Buttigieg, an Indiana mayor who was virtually unknown a few months ago.

The number Biden reported is a large sum that is sure to place him in the top fundraising bracket in the crowded primary, which has drawn over 20 candidates. But he was nonetheless outraised by Buttigieg, the mayor of South Bend, who barely registered as a blip on the national radar six months ago but posted an eye-popping $24.8 million second-quarter haul.

It’s the latest sign that Biden’s lead in the race is fragile despite him being a well-liked elder statesman who served eight years as President Barack Obama’s No. 2.

“After just two months in this race, we have seen Americans in every corner of the country chip in to join this battle for the soul of our nation,” campaign manager Greg Schultz said in a statement, noting that Biden entered the race in late April which gave him a late fundraising start.

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Democratic presidential candidate South Bend Mayor Pete Buttigieg speaks during the Democratic primary debate hosted by NBC News at the Adrienne Arsht Center for the Performing Arts, Thursday, June 27, 2019, in Miami, as former vice president Joe Biden watches. Wilfredo Lee/Associated Press

Second-quarter fundraising numbers don’t need to be reported to the Federal Election Commission until July 15, but often campaigns give an early glimpse, particularly if they had a good haul.

President Donald Trump’s campaign on Tuesday reported a massive second-quarter haul of $105 million.

In addition to Biden and Buttigieg, Vermont Sen. Bernie Sanders also reported a large figure, pulling in $18 million and transferring an additional $6 million from other accounts. Yet to be seen are highly anticipated figures from Massachusetts Sen Elizabeth Warren and California Sen. Kamala Harris, who saw a fundraising surge after her breakout performance during last week’s Democratic debates.

Sanders’ campaign manager, Faiz Shakir, attributed the campaign’s cash gulf to Sanders’ rejection of high-dollar fundraisers, which Buttigieg has embraced. Instead, Sanders’ campaign is fueled by small-dollar online donations from a blue-collar base, he said.

“It is the kind of support that we would take any day of the week over cushy, closed-door, high-dollar fundraisers in New York City, in which people eat Parmesan-encrusted salmon on a toothpick,” Shakir said.

Buttigieg’s campaign didn’t immediately respond to a request for comment.

Biden, the presumed front-runner, is coming off several shaky weeks, including a dramatic moment on the debate stage during which he struggled to respond to pointed questions from Harris about his past positions on school busing.

A member of his finance team, California attorney Thomas McInerney, withdrew his support, pointing to Biden’s recent comments highlighting his work with segregationists in the Senate .

Biden’s campaign said in an email to supporters on Monday that they “blew our fundraising goal out of the water” but remain coy about how much he raised. Harris, meanwhile, took in $2 million in the 24 hours after her searing critique of Biden.

The former vice president’s supporters say they aren’t worried.

“Let’s be honest: When you are the far and away front-runner, everybody is shooting at you,” said Steve Westly, a Silicon Valley venture capitalist who is raising money for Biden and predicted his campaign would post a large figure.

Fundraising success, however, does not equate to votes, and the race is still in the early stages. Buttigieg, for example, is winning favor among donors but has struggled with black voters, a key constituency for any winning Democratic presidential campaign.

On Tuesday, the 37-year-old acknowledged the needs to meet more voters in the black community during a campaign appearance in Chicago, suggesting that they may warm up to him if they “see me in action for a longer period of time.”

A clearer picture of the race will emerge once the numbers are reported, laying bare the relative health of the candidates’ campaigns. Candidates must reach 2% in at least four polls in addition to collecting contributions from at least 130,000 donors to appear on the September debate stage.

At least a dozen of the more than 20 campaigns are trying to lure in new donors to qualify for the fall round of debates. But the dry summer months, when fundraising is difficult, lie ahead.

Former Colorado Gov. John Hickenlooper is one of the most vulnerable candidates, in part because of his trouble raising money. He’s resisting pressure from his staff to scrap his flagging presidential campaign and instead run for Senate in his home state.

Fellow Coloradoan Sen. Michael Bennet said Wednesday that he raised $2.8 million, a drop compared to the totals of his rivals.