In this image taken from video and provided by Worldwide Pants, Inc., Republican presidential candidate Rick Perry presents the "Top Ten Rick Perry Excuses," on the set of the Late Show with David Letterman. AP hide caption

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Texas Gov. Rick Perry stumbled during Wednesday night's Republican presidential candidate in Auburn Hills, Mich., at one point seeking help from Rep. Ron Paul, (R-TX). Paul Sancya/AP hide caption

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GOP presidential candidates (from left) former Pennsylvania Sen. Rick Santorum, Rep. Michele Bachmann, former House Speaker Newt Gingrich, former Massachusetts Gov. Mitt Romney, businessman Herman Cain, Texas Gov. Rick Perry, Rep. Ron Paul, and former Utah Gov. Jon Huntsman, pose before a GOP presidential debate at Oakland University in Auburn Hills, Mich., on Wednesday. Paul Sancya/AP hide caption

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Republican presidential candidate Rick Perry holds up a postcard representing his flat tax plan Tuesday in Gray Court, S.C. Perry toured the factory and then highlighted an optional 20 percent flat tax and a deficit reduction plan.

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Joe Allbaugh, left, speaks to the press in Austin, Texas, in this Jan. 4, 2001, photo after being named as director of the Federal Emergency Management Agency by then President-elect George W. Bush.

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