Hillary Clinton's "inevitability" became less certain after a debate in Philadelphia at Drexel University in October 2007. William Thomas Cain/Getty Images hide caption

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Republican presidential candidates jockeyed for airtime when they met for their first prime time TV debate on Saturday night in South Carolina. Alex Wong/Getty Images hide caption

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HANOVER, NH - OCTOBER 11: (L-R) Jon Huntsman, U.S. Rep. Michele Bachmann (R-MN), Texas Gov. Rick Perry, Herman Cain and Mitt Romney laugh during the Republican Presidential debate hosted by Bloomberg and the Washington Post on October 11, 2011 at Dartmouth College in Hanover, New Hampshire.

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Herman Cain (right) speaks as Texas Gov. Rick Perry looks on during a GOP presidential debate at Dartmouth College on Oct. 11.

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Former Massachusetts Gov. Mitt Romney maintained his frontrunner status in the GOP presidential debate at Dartmouth College on Tuesday.

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If he decides to enter the GOP presidential race, New Jersey Gov. Chris Christie could learn a few things from fellow Gov. Rick Perry's troubles on the campaign trail.

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Herman Cain speaks prior to Florida's straw poll at the Orange County Convention Center on Saturday in Orlando. Cain was a clear winner in the non-binding poll. Mark Wilson/Getty Images hide caption

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Republican presidential candidate former Massachusetts Gov. Mitt Romney (left) passes behind Texas Gov. Rick Perry during a break in a Republican debate Monday in Tampa, Fla. Mike Carlson/AP hide caption

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