SuperPACs, the independent political groups that operate outside the usual contribution limits, are playing a critical role in the Republican presidential contest.
That's especially true in Florida, where a superPAC supporting former Massachusetts Gov. Mitt Romney helped carry him to victory in Tuesday's primary.
Now, Senate Democrats, led by New York's Charles Schumer, chairman of the Senate Rules Commitee, say they're going to investigate superPACs and the rules that govern them.
In Florida, the Restore Our Future superPAC, which backs Romney, hammered former House Speaker Newt Gingrich, placing some 7,000 ads on the Florida airwaves.
That's significantly more than aired by Romney's own campaign committee. Gingrich and his superPAC, relatively underfunded, couldn't begin to compete.
Restore Our Future filed its final financial report for 2011 Tuesday, showing that its total fundraising surpassed $30 million.
Seven donors gave $1 million each. And more than 40 corporations and other businesses contributed.
This is the kind of thing that Democrats in the Senate want to investigate.
"We're going to seek to hear from stakeholders behind these groups. And perhaps also those contributing to them," said Schumer. "We want to look at possible ways to enhance disclosure ... and also to improve the rules that prevent coordination between the outside groups and the campaigns themselves."
The year-end reports show another conservative superPAC looming even larger than Restore Our Future.
That's American Crossroads, along with its sibling, a nonprofit entity called Crossroads GPS.
Their spokesman, Jonathan Collegio, tells NPR that combined they raised some $51 million over the past year.
Among the donors to American Crossroads, Texas businessman Harold Simmons gave $5 million.
But about two-thirds of the $51 million in total contributions went to Crossroads GPS. And as a nonprofit organization, not a superPAC, it never has to disclose its donors.
Crossroads GPS does so-called issue ads. Its new ad is about Solyndra, a failed solar manufacturer with ties to the Obama administration. The ad calls on viewers to "tell President Obama, we need more jobs not more insider deals."
And Crossroads GPS even has its own issues platform, suitable for use by House and Senate candidates.
"I think that what we're doing here is unique, in that Crossroads GPS does spend significant resources advocating for those policy prescriptions in the news media, in the paid media and across social media platforms," said Collegio.
But in the liberal camp, superPACs and issue groups aren't nearly so popular.
One leading superPAC is Priorities USA Action, supporting President Obama.
Right now it's going after Romney on Spanish-language radio, with an ad that says Romney "might have two faces, but we know all too well who the true Mitt Romney is."
Priorities USA Action raised barely $3 million last year. Its head, former Obama aide Bill Burton, says it's just a matter of when those liberal donors come through the door.
But there are other places for Democrats to contribute.
One is the Obama campaign and another is the Democratic National Committee, which can help Obama even more than a superPAC.
Last year, the president, without much publicity, coaxed donors to give some $92 million.
Week-by-week fundraising from candidates and superPACS in the last quarter of 2011.
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