Bernie Sanders is offering Hillary Rodham Clinton an unexpected challenge in the race for primary campaign money this quarter as he collected nearly as much money from small donations as the Democratic front-runner has from big-dollar donors.

The Vermont senator's campaign says he has raised about $26 million for his presidential campaign in the past three months. Coming mostly from small donations given online, the sum underscores the draw of his insurgent campaign among the grassroots of the Democratic Party.

Clinton's campaign, in its own announcement Wednesday, said she had taken in $28 million. Most of it came from fundraisers hosted by big donors across the country. Many took place in the traditionally Democratic treasure-chests of Manhattan and Hollywood. She raised at least $19 million from about 60 events where admission typically cost $2,700, the biggest donation allowed by law.

The Sanders campaign has held just seven traditional fundraisers since launching at the end of April, said Sanders campaign spokesman Michael Briggs, compared to a total of more than 110 for Clinton over the same period.

Hours after initially announcing a take of $24 million, Sanders' team boosted the total by an additional roughly $2 million. The campaign said donations rolled in all day Wednesday, the result of tweets and emails imploring supporters to give before the midnight close of the fundraising period.

"We have a chance to send an unmistakable message about the size and strength of our campaign," Sanders tweeted, urging supports to donate. With just a few hours left in the day, he emailed supporters, "Chip in $3 before the midnight FEC deadline as a way of saying you have had enough of the billionaire class buying our elections."

Sanders may be the biggest beneficiary of using Twitter as a campaign donation tool, which was rolled out in mid September. As The Christian Science Monitor reported:

As of June, 77 percent of Democratic candidate Bernie Sanders’ campaign had been financed by small donations. Republican campaigns by Ben Carson and Donald Trump have also benefited from small donations at 65 and 44 percent, respectively. Although these candidates have already had small-donation success, everyone agrees that this new partnership could be a game-changer. “There hasn’t been to this point a lot of success with an application that makes it possible for you to quickly and easily and simply make contributions without leaving the platform itself. That’s the key difference and why we’re so excited to test this,” said Matt Compton, digital director at the Democratic National Committee.

Clinton's total for the past three months marks a notable drop-off from the $47.5 million she raised during the previous fundraising period, despite a busy schedule of donor events and an active online push for dollars.

The sum is almost exactly what she brought in during the same period during her 2008 bid for the Democratic presidential nomination. But there's a key difference: In the previous campaign, she simultaneously raised money for the primary and general election, the latter of which she wasn't able to use after losing the nomination to Barack Obama.

This time, Clinton is raising only money for the primary election — meaning she can use every penny in her bid to secure her party's nomination.

Clinton's campaign has set a goal of bringing in $100 million by the end of the year, a sizable amount intended to fund the hundreds of staffers and massive infrastructure her team has placed across the country.

Aides said they were happy with the $75 million the campaign has raised so far.

"Thanks to our supporters, we are able to meet our goals and build an organization that can mobilize millions of voters to ensure Hillary Clinton is their fighter in the White House," campaign manager Robby Mook said in a statement.

The nearly $20 million decline is partially attributable to the typical summer fundraising slow-down. Some donors are also waiting to see if Vice President Joe Biden joins the race. In previous campaigns, Biden was not known as an aggressive fundraiser and should he enter this year, he would have to raise tens of millions in a matter of weeks just to catch up with his primary opponents.

Sanders' campaign says it ended the latest fundraising quarter with more than $25 million in the bank. Clinton did not release the total amount in her account. But she's been spending money at a rapid clip, using up 40 percent of the $47 million in donations she had amassed by the end of June.

Sanders campaign strategist Tad Devine said the campaign had surpassed the pace that Obama set during the 2008 primary season in terms of sheer numbers of donors. Because most of those givers hadn't maxed out their donations, he said the campaign could return to them in the months ahead to raise more money.

"For Bernie Sanders to get into this race on the 30th of April and to be raising almost as much money as Hillary Clinton is a significant achievement," Devine said. He said the cash infusion would give the campaign "enormous flexibility."

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Associated Press writer Julie Bykowicz in Washington contributed to this report.

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