WASHINGTON -- An outside group founded this spring by two former Obama White House advisers has raked in millions in donations since April, relying in part on top-flight fundraisers and labor unions to counter GOP-leaning ads this summer critical of the president and congressional Democrats.

Priorities USA Action, an independent group founded by former Obama aides Bill Burton and Sean Sweeney, said Sunday its donations included $2 million from film producer Jeffrey Katzenberg, as well as $500,000 each from Newsweb founder Fred Eychaner and the Service Employees International Union.

Priorities USA Action and sister Priorities USA have raised more than $5 million since this spring, Burton said Sunday. Those amounts paled in comparison to the $86 million raked in by the Democratic National Committee from April through June, as top donors focused on President Obama's first fundraising quarter.

Burton said Priorities has had a major impact with targeted local advertisements -- tallying more than $700,000 -- in part by making Medicare cuts a litmus test for Republican presidential candidates. That included a targeted ad against former Massachusetts Gov. Mitt Romney on Medicare.

Priorities' ad buys contrast the $20 million to be spent this summer by Republican-leaning American Crossroads -- tied to former President George W. Bush adviser Karl Rove -- on a series of ads critical of Democrats ahead of the November 2012 election.

In response to "Rove's negative ads on the economy," Burton said, "we choose to invest in only swing states and, within those states, the most efficient television markets. Dollar for dollar, our spending is having a much greater impact on the voters who will decide the 2012 race."

The group planned to file its report with the Federal Election Commission on Sunday.

Both the Democratic- and GOP-aligned groups, known as "super" political action committees, have gained momentum following the Supreme Court's 2010 ruling in Citizens United v. Federal Election Commission, which overturned a previous ban on corporate spending in federal elections.

Obama has publicly criticized the ruling -- even at a 2010 State of the Union address with court members a stone's throw from the House rostrum -- but that hasn't stopped Democratic-leaning groups from trying to keep up with an influx of spending by new GOP-leaning groups, including Crossroads.

Indeed, wealthy donors have flooded donations to GOP-leaning super PACs, but labor unions and activists have also opened their checkbooks, an Associated Press review of FEC records found. Democratic-tilting American Bridge, for instance, received a bulk of its $3 million from liberal congressional districts in New York City and the San Francisco Bay Area.

Crossroads, meanwhile, raised $105,000 within the last two weeks, more than 95 percent coming from the John Templeton Foundation, FEC records show. Templeton Foundation President John Templeton Jr. himself contributed the maximum $5,000 to America's Foundation, the political action committee of former GOP Sen. Rick Santorum, a 2012 candidate for the White House.

Crossroads Spokesman Jonathan Collegio said the group's nonprofit arm, registered as a 501(c)(4) social-welfare organization by the IRS, would be "more active" than Crossroad's main 527 group.