In announcing its fund-raising total, the Biden campaign emphasized how much it had raised per day that Mr. Biden was in the race, a statistic that puts him above Mr. Buttigieg for the quarter. “We’ve raised more per day than any other presidential campaign,” Mr. Biden’s team wrote in an email to supporters, with the subject line “INCREDIBLE milestone.”

The fund-raising haul was announced hours before Mr. Biden and his wife, Jill, kicked off a swing through Iowa, where they will be spending the Fourth of July holiday campaigning.

Mr. Biden has been the clear leader in early national polling, though he has slid somewhat in recent surveys. At the same time, Senator Kamala Harris of California has found momentum after last Thursday’s debate, at which she confronted Mr. Biden over his comments about segregationist senators and his record on school busing. Ms. Harris, who raised more money than anyone aside from Mr. Sanders in the first quarter of the year, has not yet revealed her fund-raising total for the second quarter, but she is expected to disclose a sizable number as well.

[We tracked down the 2020 Democrats and asked them the same set of questions. Watch them answer.]

Mr. Biden does not appear to be slowing his high-dollar fund-raising pace this month, with finance events scheduled for New York and Los Angeles in coming weeks, according to invitations reviewed by The New York Times.

Mr. Biden has devoted considerable time to high-dollar fund-raisers since joining the race, allowing him to scoop up huge amounts of campaign cash. But his time on the fund-raising circuit also carries the risk that he will be perceived as focused on wealthy donors at a time when small online donations are coveted by Democratic campaigns.

Mr. Sanders’s campaign, in particular, has sought to highlight how Mr. Biden is raising money.

“Here’s the truth: Joe Biden is traveling around the country raising a lot of money for his campaign at fund-raising events with billionaires, corporate lobbyists and Wall Street executives,” Mr. Sanders’s campaign manager, Faiz Shakir, wrote in an email seeking donations last month. “And we can’t afford to fall too far behind.”

It was at a fund-raiser in New York last month that Mr. Biden cited two segregationist senators as he recalled a time of “civility” in the Senate, remarks that have drawn criticism and put a spotlight on his opposition to school busing early in his Senate career. (Mr. Biden allows reporters into all of his fund-raisers, unlike other major Democratic candidates who are holding high-dollar events.)

Mr. Biden had been expected to post a big number for the second quarter. His campaign said it brought in $6.3 million in the 24 hours after Mr. Biden entered the race on April 25, more than any other campaign had disclosed raising in its first day.