Bill Koch (center) celebrates his team's 1992 America's Cup win. Koch, the brother of billionaire GOP donors Charles and David, has given $2 million to the superPAC backing Mitt Romney. Vince Bucci/AFP/Getty Images hide caption

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PayPal co-founder Peter Thiel, who has donated more than $2.5 million to a superPAC backing GOP presidential candidate Ron Paul, speaks at the National Press Club in Washington, D.C., in October. Chip Somodevilla/Getty Images hide caption

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Dreamworks Animation CEO Jeffrey Katzenberg, shown at CinemaCon 2012, has donated $2 million to the pro-Obama superPAC Priorities USA Action. Chris Pizzello/AP hide caption

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Some superPAC donors are hiding from public scrutiny. hide caption

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Hedge fund manager Paul Singer of Elliott Management has donated $1 million to Mitt Romney's superPAC. Lucas Jackson/Reuters/Landov hide caption

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In a video from the Horatio Alger Association, William Doré tells of a tense and abusive childhood. Horatio Alger Association/YouTube hide caption

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J.W. Marriott dines with his son Bill in a Hot Shoppe in March 1969. The elder Marriott was close to Mitt Romney's father, George. Dennis Brack /Landov hide caption

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Foster Friess introduces Rick Santorum at the 2012 CPAC Conference in Washington, D.C., on Feb. 10 wearing a sweater vest embroidered with the candidate's name. Ron Sachs/CNP DPA/Landov hide caption

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Bill Maher, shown here at a 2011 event in Los Angeles, gave $1 million to the superPAC supporting President Obama's re-election bid. Chris Pizzello/AP hide caption

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Texas businessman Harold Simmons stands outside a Dallas courthouse in this 1997 photo. Flor Cordero/Reuters /Landov hide caption

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Sheldon Adelson speaks at the 2008 "Facing Tomorrow" Presidential Conference in Jerusalem. David Silverman/Getty Images hide caption

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