WASHINGTON — When Pete Buttigieg’s top fund-raisers gathered in Miami Beach to watch the first Democratic debate last week, those in attendance included corporate executives, Chelsea Clinton’s wedding planner and a 19-year-old who had started a viral Facebook page supporting the South Bend, Ind., mayor’s presidential campaign.
It was a diverse group of supporters, but not a surprising one for Mr. Buttigieg. Through the first two fund-raising quarters, no other Democratic presidential candidate has married traditional high-dollar fund-raising with online small donations as successfully as Mr. Buttigieg, whose campaign announced on Monday that he had collected $24.8 million from more than 294,000 donors for the three-month period ending Sunday.
While former Vice President Joseph R. Biden Jr. has tapped into the party’s major donors, and Senators Bernie Sanders and Elizabeth Warren have staked their candidacies on grass-roots support, Mr. Buttigieg has risen to the top tier by doing both, after beginning his campaign virtually unknown outside of Indiana.
His second-quarter total is likely to surpass every one of his rivals except perhaps for Mr. Biden, according to officials briefed on the candidates’ fund-raising efforts.
Mr. Buttigieg’s fund-raising haul indicates he has moved beyond the circle of L.G.B.T. donors who, early in the race, powered his bid as the first gay major presidential candidate. He has put together a wide-ranging donor base that looks more like the one Barack Obama used when he stunned observers by keeping pace with and then eclipsing Hillary Clinton’s fund-raising at the outset of the 2008 campaign.
“They’ve got a badass operation,” Rufus Gifford, the finance director for Mr. Obama’s re-election campaign, said of Mr. Buttigieg’s campaign.
During the second quarter, Mr. Buttigieg attended about 50 high-dollar fund-raising events, for which ticket prices typically run $2,800, the maximum individual contribution allowed by federal law in the primary. But he also held 20 “grass-roots” fund-raising events, for which ticket prices start as low as $15.
And from March 24 to June 22, the Buttigieg campaign’s combined spending on digital advertising on Facebook and Google ($1.3 million) exceeded that of any other candidate except Mr. Biden and Ms. Warren, according to Bully Pulpit Interactive, a Democratic digital communications firm.
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Mr. Buttigieg has wooed tech executives in Silicon Valley and, as a former Navy reservist in Afghanistan, has courted military veterans. He is also popular among educated liberals on the coasts; this weekend he will hold fund-raisers on Martha’s Vineyard and Nantucket.
Despite his success, Mr. Buttigieg’s strategy presents some challenges. Accepting Silicon Valley money has become controversial at a time when big tech companies are under siege for lapses with privacy and misinformation. And his popularity with wealthy white liberals is great for fund-raising but so far has not helped him win much support from people of color, without whom no candidate can survive key early-primary contests in the South and West.
He still faces a big challenge in growing his support with black voters, a critical constituency. He has recently been confronted by a local crisis, the fatal shooting of a black man by a white police officer in South Bend, which has tested his leadership.
Mr. Buttigieg had more than 230,000 new donors in the second quarter, bringing his total to more than 400,000, his campaign said. The average contribution over the course of his campaign has been $47.42, according to his team. His campaign said it now had more than $22.6 million in cash on hand. Of that, $832,000 is earmarked for the general election and cannot be used in the primary.
“This fund-raising report shows that Pete’s message is resonating with Americans, and it’s proof that we are building an organization that can compete,” Mike Schmuhl, his campaign manager, said in an early-morning email to supporters announcing the fund-raising total.
Mr. Buttigieg’s rivals have mostly favored one fund-raising approach or the other. Mr. Biden has concentrated his efforts on the broad network of Obama donors in major cities, but the 76-year-old former vice president hasn’t energized the small-dollar grass-roots world. Mr. Sanders and Ms. Warren have sworn off closed-door big-donor events as a political strategy aimed at creating a wider universe of small donors.
Senator Kamala Harris of California, who raised the second-highest amount of money during the campaign’s first reporting period that ended March 31, is expected to raise less in the second quarter than the $24.8 million that Mr. Buttigieg announced Monday.
Last week in Miami, the Buttigieg campaign hosted a de facto retreat for the campaign’s top fund-raisers, which included strategy sessions with Mr. Buttigieg at the Miami Hilton and a debate watch party at the Miami Beach home of the home-furnishings entrepreneur Ira Statfeld.
The watch party included Mr. Buttigieg’s top fund-raising officials, known on his campaign as “investment directors”: Anthony Mercurio, a veteran of Hillary Clinton’s 2016 campaign and Michael Bloomberg’s gun control group; and Swati Mylavarapu, a Silicon Valley venture capitalist who attended Harvard with Mr. Buttigieg and spent a year at Oxford with him when they were Rhodes scholars.
Also in attendance was Lucas Carroll, a Boston College undergraduate who in January started a “Pete Buttigieg for President” Facebook page and then used it to raise about $35,000 for the campaign. Between his freshman and sophomore years, Mr. Carroll is spending the summer as a fund-raising intern at Mr. Buttigieg’s headquarters in South Bend.
“It’s a young campaign,” said Bryan Rafanelli, a Democratic fund-raising veteran from Boston who planned Chelsea Clinton’s 2011 wedding and hosted a Fenway Park event for Mr. Buttigieg. “This wasn’t a room filled with Obama and Clinton finance people.”
But there a lot of Obama fund-raisers involved, many of them former ambassadors.
Tod Sedgwick, who was Mr. Obama’s ambassador to Slovakia, is among a group of former diplomats who are bundling contributions for Mr. Buttigieg. David Jacobson, Mr. Obama’s ambassador to Canada, is hosting a fund-raiser for Mr. Buttigieg in Chicago Tuesday. Timothy Broas (the Netherlands), John Phillips (Italy) and Bill Eacho (Austria) have also raised money for Mr. Buttigieg.
“Obama tended to have the larger bundlers, and they would have campaign events every quarter,” Mr. Sedgwick said. “These guys have a national investment council and they pretty much add anyone who they think is making an effort to raise money.”
After suspending most of his fund-raising schedule the last two weeks to attend to protests over the police shooting and to prepare for the debate, Mr. Buttigieg is back on the road this week. Mr. Jacobson is hosting a high-dollar event in Chicago on Tuesday. In Massachusetts, there is a $2,800-per-ticket event Friday in Provincetown, a $250 brunch Saturday on Nantucket and a $2,800 breakfast on Nantucket. Those high-dollar events are bracketed around a “grass-roots” event Saturday afternoon on Martha’s Vineyard for which tickets start at $15.
The campaign raised $1.1 million from grass-roots events and another $550,000 from small-dollar bundlers, an official said.
“They are innovating every single minute of every single day,” said Brendan Mullen, a cybersecurity executive who was the Democratic nominee for South Bend’s House seat in 2012 and who attended the campaign’s Miami debate events. “I’ve never seen anything scale at the speed they are. It’s scaling faster than any start-up in the history of America.”
Mr. Buttigieg’s finance team has grown from three employees at its outset to 28, with staff members in most major markets and several devoted to online and grass-roots events.
When he began his campaign, Mr. Buttigieg would tell prospective donors he was not “asking for monogamy” in terms of whose campaign they supported. In recent weeks, his top fund-raising aides have been trying to pick off donors and bundlers who have committed to other candidates in the race, offering private meetings with Mr. Buttigieg.
Kevin Johnson, a West Point graduate and renewable energy executive who is co-hosting the Chicago fund-raiser with Mr. Jacobson, said Mr. Buttigieg has tapped into the network of military veterans.
“I’m not a historical donor like other folks, like Mr. Jacobson, and the campaign has welcomed me in,” Mr. Johnson said. “I’m helping to bring in other veterans of color, and other veteran entrepreneurs of color that Pete’s message speaks to.”
Mr. Buttigieg’s fund-raising totals are short of what Mr. Obama and Mrs. Clinton raised at the same juncture of their 2008 campaigns. During the second quarter of 2007, Mr. Obama collected $33 million, while Mrs. Clinton took in $27 million. Both were more widely known than Mr. Buttigieg.
Still, Mr. Buttigieg’s total for the most recent quarter is more than three times what he raised in the first quarter, $7.1 million, which itself was an attention-grabbing figure that offered early evidence that his candidacy was catching on.
Mr. Buttigieg is the first Democratic candidate to announce his fund-raising total for the second quarter. Other candidates will most likely publicize their numbers in the coming days, and all of them are required to report their fund-raising to the Federal Election Commission by July 15.
Mr. Buttigieg’s fund-raising pace is likely to allow him to remain in the race as long as he wants, a stunning turn of events for a candidate who began his exploratory campaign with a list of 24,000 email addresses and a staff of five people.
“Our dogs have more followers now on social media than I had in January when we got into this,” Mr. Buttigieg said during a recent interview. “The trajectory has been dizzying. We actually needed to level off because if it stays that dizzying, we’ll lose our balance.”