The president's campaign, The New York Times reported, has struggled to bring in the big contributions it's seeking for a race against Mitt Romney, with declines in the amounts given by traditional major sources of campaign money for Obama, including the financial, medical and legal industries as well as Hollywood.
As a result, the Obama campaign has been forced to rely more on small contributions.
Federal campaign finance filings show Obama's re-election campaign in March raised $46.4 million and spent $37.7 million, excluding money raised with the Democratic National Committee, Politico reported.
Obama and the Democratic National Committee ended March with about $130 million in cash on hand, much more than Romney and the Republican National Committee.
But the Times noted contributions from major sources to Obama's campaign have fallen off since 2008, and that has left aides and supporters worried Republicans and their super PACs will hold a major fundraising advantage by fall.
"[Obama campaign officials] are feeling the pressure," an Obama fund-raiser said. "They're behind where they expected to be. You have to factor in $500 million-plus in Republican super PAC money."
Federal documents also showed the Campaign for Primary Accountability, a super PAC that has targeted incumbent members of Congress, had raised more than $645,000 in March, Politico said.
The group spent almost $800,000 last month, mostly targeting incumbents in competitive races, and had $437,807 cash on hand at the end of March.