Hillary Clinton's closest challenger for the 2016 Democratic nomination managed to raise almost as much campaign cash over the last three months as the party's front-runner.

Sen. Bernie Sanders, I-Vt., is drawing huge amounts of small-dollar donations online, illustrating that his campaign is focused on face-to-face meetings with potential voters and not on courting big-time contributors, the Washington Post noted.

Since July, Sanders has raised more than $24 million, a significant figure that tops the campaign's initial goals, an unidentified aide told Time. The 650,000 individual contributors that have given to the senator even exceed the total number of supporters that had written checks to Barack Obama's 2008 campaign at this point in the election cycle, the magazine added.

"It is an objective measure of how far the campaign has come in a very short time," Sanders campaign adviser Tad Devine said. "If we continue to build on this we will not only have resources for the front end of the campaign, we will have built an infrastructure ... when we move into the national campaign on Super Tuesday."

Just before the quarterly disclosure deadline on Wednesday, Sanders took in yet another $2 million -- a fact that further worried the Clinton camp, which has touted its own number of small donations, but has also held big-dollar fundraisers, the Atlantic noted.

"This deadline is an opportunity to send a powerful message to the political media and the super PACs attacking us about the strength of our campaign," the Sanders campaign said on social media.

His fundraising success is not the first surprise from Sanders during the 2016 race, in which Clinton was once widely seen as the automatic Democratic nominee. In July, the former Burlington, Vermont mayor managed to draw a crowd of more than 10,000 supporters to a campaign event at the Veterans Memorial Coliseum in Madison, Wisconsin, CBS News recalled.

"Tonight, we have more people at any meeting for a candidate of president of the United States than any other candidate," Sanders said at the event. "We believe that the time has come when people ... create a political movement which says to the billionaire class, 'You can't have it all,'"