WASHINGTON Restore Our Future, an outside "Super PAC" backing Republican presidential hopeful Mitt Romney, raised $3.9 million in April, less than half the haul it collected in March, the group's financial disclosures showed on Sunday.
But the "super" political action committee still emerged with $8.2 million in cash on hand at the end of last month - more than it did in March - after spending $2.9 million, according to the filing with the Federal Election Commission.
In March, the deep-pocketed Super PAC brought in $8.7 million and had $6.5 million left in cash on hand.
Restore Our Future has become a formidable force in Romney's effort to defeat Democratic President Barack Obama in the November 6 election.
Although the group cannot coordinate with the campaign, it has been taking advantage of its ability to raise unlimited funds and investing millions into advertising wars first against Romney's rival Republican candidates and to promote Romney as a better alternative to Obama.
Romney emerged as the presumed Republican nominee in April as he started fundraising alongside the Republican Party and his intramural challengers faded into the background.
"The Super PAC now doesn't become important until you have to run advocacy ads of the kind that the campaign can't run," said Fred Zeidman, one of Romney's top fundraisers.
"A lot of the focus in recent weeks has been on the Victory Fund," he said, referring to the joint fundraising fund launched in April that can accept up to $75,800 per contributor and offers donors another venue of giving large sums to Romney.
Campaigns on their own can take in $2,500 during the primary process and another $2,500 for the general election.
Restore Our Future, which counts more than a dozen donors who have given $1 million or more, last month scored another seven-figure donation from Fort Worth, Texas, hedge fund manager John Kleinheinz.
Harold Hamm, chief executive of oil production firm Continental Resources Inc., who recently became Romney's top energy adviser, contributed $985,000.
Stephen Zide, a managing director at Bain Capital LLC, a private equity firm co-founded by Romney, gave $250,000.
Houston homebuilder Bob Perry, who is one of the Super PAC's biggest donors and a known Republican financier, last month gave Restore Our Future another $750,000 but the filing shows that the donation was returned several days later.
The Super PAC helping Obama's re-election effort, Priorities USA Action, has been badly lagging its Republican rival in fundraising. Its April figures are due to be filed with the FEC by the end of Sunday.
Republicans and Democrats are racing to raise as much money as possible for advertisements and get-out-the-vote efforts, projected to total $1 billion on each side of the aisle.
Super PACs, spawned by a 2010 U.S. Supreme Court decision, have already spent more than $100 million trying to influence congressional and presidential races this campaign cycle.
Republicans have taken a strong lead in the Super PAC game because many Democrats opposed the court decision and have remained hesitant to donate to the groups that have largely taken over the dirty work of negative advertising.
Facing no challengers within the Democratic Party, Obama for months maintained strong fundraising advantage over Romney, but it has started to shrink in April as Republicans began to coalesce behind Romney.
Last month, Obama's campaign and its Democratic allies raised $43.6 million and said there was $115 million in the bank. Romney and the Republican party said they raised $40.1 million and had $61.4 million left in cash on hand.
Two of Romney's rivals - Ron Paul and Newt Gingrich - ended their challenging bids in May, when Paul raised $2 million, ending April with $2.5 million left on hand and no debt.
Gingrich dropped out on May 2 after closing out April with $806,951 in cash on hand and $4.8 million in debt. His campaign raised a paltry $638,831 last month.
Santorum, who ended his campaign on April 10, raised $1.2 million that month, ending it with $1 million left in cash on hand and $2.3 million in debt.
Another group helping Romney catch up to Obama in fundraising is American Crossroads. Working alongside its non-profit sister group Crossroads GPS, the Super PAC has plans to spend up to $300 million this campaign season, and two-thirds of it on defeating Obama.
The Crossroads groups were conceived in part by Karl Rove, chief strategist of Republican George W. Bush's two presidential election wins. Crossroads GPS, the non-profit, is not legally required to report its fundraising or donors to the FEC.
(Additional reporting by Patrick Temple-West; Editing by Eric Walsh)