"Ninety-eight percent of our contributions are under $250," Axelrod said. "The average contribution is around $51. It would take 181,000 of our contributions to match one of those anonymous contributions. That's just a concern not just for us but for our democracy."

Democrats have struggled to attract similar high-dollar donations to their outside groups, with most liberal millionaires and billionaires thus far opting to remain on the sidelines. That's despite the president's high-profile reversal on super-PACs in Feburary.

"With so much at stake, we can't allow for two sets of rules in this election whereby the Republican nominee is the beneficiary of unlimited spending and Democrats unilaterally disarm," campaign manager Jim Messina said in a statement at the time. "Therefore, the campaign has decided to do what we can, consistent with the law, to support Priorities USA in its effort to counter the weight of the GOP super-PAC."

On Thursday, Axelrod said the president would push for campaign finance reform if he won a second term.

"I hope that when we win this election, one thing we can do is bring some common sense back to our system," Axelrod said.

The senior Obama adviser also admitted that President Obama could likely become the first incumbent to be surpassed in fundraising dollars. Not only has the Romney campaign benefited from tens of millions of dollars donated to his super-PAC, but in May the Republican challenger's campaign itself posted a better haul than President Obama.

"We will be the first presidential campaign, the incumbent president to be outspent in an election campaign," Axelrod said. "I think it will be by more than a little bit. That's something that's never happened before."