Wisconsin Gov. Scott Walker speaks at the Western Conservative Summit, hosted by the Centennial Institute, Colorado Christian University's think tank, in Denver, last month. Walker is announcing a run for the White House, joining more than a dozen Republicans to enter the 2016 contest. Brennan Linsley/AP hide caption

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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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On the day he revised his tax plan to 9-0-9, Republican presidential candidate Herman Cain signs a supporter's "999" sign after unveiling his "Opportunity Zone" economic plan in front of the Michigan Central Station, an abandoned train depot in Detroit.

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Left to right: Former Sen. Rick Santorum; Rep. Michele Bachmann; former House Speaker Newt Gingrich; former Massachusetts Gov. Mitt Romney; Rep. Ron Paul; former Minnesota Gov. Tim Pawlenty; entrepreneur Herman Cain. Emmanuel Dunand /AFP/Getty Images hide caption

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NPR's Ari Shapiro on 'Morning Edition'

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