WASHINGTON — President Barack Obama's national campaign co-chairman, Chicago Mayor Rahm Emanuel, is stepping down to help raise money for a "super" political committee supporting Obama. The move reflects increasing alarm by Democrats being outspent by Republican presidential nominee Mitt Romney and shows that despite legal limits, the lines between campaigns and super PACs are blurry.

The campaign and the super PAC confirmed Wednesday that Emanuel – once one of Obama's closest White House aides – is joining Priorities USA Action, which is run with the help of other former White House advisers and has spent millions of dollars on ads to help the president. Emanuel brings fundraising gusto to an operation that so far has trailed its GOP counterparts in the money race, partly because some prominent Democratic donors including financier George Soros consider super PACs distasteful.

The move adds another wrinkle to Obama's evolving positions on how elections are funded. Campaign spokeswoman Jen Psaki said Wednesday that while Obama opposes the Supreme Court's 2010 Citizens United case that all but unraveled campaign-finance laws, he needs to use all available tools for raising money.

"We're not going to bring a butter knife to a gun fight," she said.

Obama raised a remarkable $750 million four years ago, but his advisers now acknowledge that the incumbent likely will be outspent this time.

The influence of money in politics has received heightened scrutiny this election cycle as super PACs have spent hundreds of millions of dollars to support their favored candidates. This is the first presidential election that is highlighting the impact of these groups.

Super PACs are allowed to raise unlimited money for candidates, but they are supposed to remain separate from the campaigns they support and not coordinate with them.

Federal Election Commission regulations require officials who are "materially involved" in decisions about super PAC finances to be independent from the candidate. That is why Emanuel officially resigned from Obama's campaign.

"It meets the current, pathetic legal definition of `independent,' not the common-sense one," Trevor Potter, a former FEC commissioner and a staunch advocate of campaign finance reform, said of the Emanuel switch.

FEC rules largely prohibit paid employees and independent contractors of campaigns from working for a super PAC within 120 days of leaving that campaign. Emanuel was a volunteer for Obama's campaign so that prohibition does not apply to him.

In an interview, Bill Burton, the political committee's senior strategist, said of Emanuel, "It's good to have him on our team and to have his expertise, allowing our donors to listen to our message in a new way."

Burton said Emanuel's only role would be fundraising and the mayor wouldn't help make strategic decisions about where to spend money.

Priorities USA Action has raised about $25.5 million through July plus an impressive $10 million last month, the group said. Still, it lags similar Republican-leaning groups in overall fundraising; those super PACs hope to raise more than $300 million by November to pay for ads assailing Obama or supporting his GOP challenger, Mitt Romney.

Emanuel has been Obama's right hand man in the White House and served as his first chief of staff. He called Obama a "once-in-a-generation president" in his remarks to delegates Tuesday at the Democratic National Convention. And on Wednesday, he planned to stop by first lady Michelle Obama's private skybox at the convention, according to the White House.

A spokeswoman for Emanuel declined to comment to The Associated Press. Emanuel told The Washington Post that he was "helping, not running" the super PAC.

Such close relationships between candidates' advisors and super PACs have happened on the Republican side, too.

Restore Our Future, a pro-Romney super PAC that's spent more than $90 million so far, is run with the help of former Romney campaign adviser Carl Forti. He also consults for American Crossroads, the GOP-supportive super PAC run with the help of Karl Rove, adviser to former President George W. Bush.

Those interactions have also drawn criticism. Rove appeared at a Romney campaign fundraising retreat in Park City, Utah, this summer. Rove and Romney adviser Ed Gillespie also hosted a closed-door political briefing with top donors last month in Colorado.

Spending by campaigns, parties, super PACs and other outside groups in this presidential campaign will likely approach $2 billion by November by both parties combined.

Earlier this week, two people familiar Romney's fundraising efforts said his campaign and the Republican Party raised at least $100 million in August, hitting that figure for the third consecutive month. They spoke on condition of anonymity because they were not authorized to share internal campaign matters; the campaign says it will release its official numbers next week.

Romney and the GOP raised a combined $101 million in July, $106 million in June and $76.8 million in May. For their part, Obama and the Democrats pulled in $75 million last month, and $71 million in June and $60 million in May.

PACs like American Crossroads and Restore Our Future – buoyed with the support of wealthy donors – have spent tens of millions of dollars on TV ads critical of Obama in key states, and the groups expect to spend much more as November approaches. Another pro-Obama super PAC, American Bridge 21st Century, has raised millions of dollars, but it instead focuses much of its efforts on so-called opposition research critical of the GOP.

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