"Exploratory" Republican presidential candidate Jeb Bush speaks April 17 at the First in the Nation Republican Leadership Conference in Nashua, N.H. His super PAC — Right to Rise — is aiming to raise $100 million dollars by June 1. Brian Snyder/Reuters/Landov hide caption

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Sen. Rand Paul, R-Ky., center, meets with members of the Londonderry Fish and Game Club in Litchfield, N.H., on Jan. 14. Paul was one of three GOP presidential hopefuls who attended Sunday's semiannual gathering of David and Charles Koch's donor network in California. Jim Cole/AP hide caption

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Comedian Stephen Colbert, left, holds a rally with former GOP presidential candidate Herman Cain at the College of Charleston in South Carolina. Richard Ellis/Getty Images hide caption

itoggle caption Richard Ellis/Getty Images