(CNN) -- This election season, the term "Super PAC" has escaped from the obscure world of campaign finance lawyers to emerge on the front pages of major newspapers and political websites. Super PACs are political organizations that can take unlimited sums from individuals, corporations and labor unions to spend in support of, or opposition to, federal candidates. To do so legally, a Super PAC must avoid  certain forms of coordination with candidates. The groups played a big role in Iowa, with a pro-Mitt Romney Super PAC, "Restore Our Future," widely credited with running ads that halted Newt Gingrich's momentum in the polls. They are expected to play an even greater role in the fall, when control of the White House, Senate and U.S. House of Representatives will be up for grabs.
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Richard Hasen: Super PACs have emerged in a big way as funders of campaign ads
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He says Supreme Court ruling opened the door to special-interest spending
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Super PACs can influence voters and put legislators in their debt, he says
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Hasen: Danger is that, after election, lawmakers will back causes of Super PAC funders
But I am concerned that Super PAC spending will influence the outcome of close @placeholder and congressional races.