Ms. Harris raised less during the campaign’s second quarter than she did in the first, which she entered three weeks into January. In that quarter, she raised almost exactly $12 million, more than any other candidate aside from Mr. Sanders.

She has pulled in large sums from online donors while also aggressively raising money on the traditional fund-raising circuit, an approach that Mr. Buttigieg is also employing with great success.

The Harris campaign said Friday that she received donations from more than 279,000 people during the second quarter and raised more than $7 million of her total online. The campaign said its average donation was $39, lower than the $49 average reported by the Biden campaign but higher than the $18 average cited by the Sanders team. Campaigns often point to small average donations as evidence that they are attracting a large pool of grass-roots supporters.

Ms. Harris’s team worked to capitalize on her strong showing at the debate last week. Her campaign said it received online donations from about 63,000 people in the first 24 hours after the debate, more than half of whom were first-time donors to her presidential bid. It was the best online fund-raising day of her campaign so far, her team said.

“As it has been from the beginning, this campaign is powered by the people,” said Juan Rodriguez, Ms. Harris’s campaign manager. “These resources will help expand Kamala’s growing strength in this primary.”

In its announcement, the campaign did not indicate how much cash it had on hand.

Ms. Harris’s advisers have spent the week since the debate aiming to extend her dispute with Mr. Biden over issues of race and school busing programs.

As post-debate polling showed her campaign on the rise, Ms. Harris’s aides took shots at Mr. Biden and his team on Twitter. And Ms. Harris said in Iowa that Mr. Biden “has yet to agree that his position on this, which was to work with segregationists and oppose busing, was wrong.”

Mr. Biden’s campaign responded that he and Ms. Harris have expressed similar positions on busing. She said Wednesday that local school districts should determine whether to bus students. Mr. Biden has said he opposed federally mandated busing but supported voluntary local programs to desegregate schools.