Wisconsin Republican Gov. Scott Walker speaks in Milwaukee in May. Newly released documents show prosecutors are alleging Walker was at the center of a nationwide "criminal scheme" to illegally coordinate with outside conservative groups. Jeffrey Phelps/AP hide caption

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Wisconsin Republican Gov. Scott Walker (right) celebrates his win over Democratic challenger Tom Barrett at Tuesday night's victory party in Waukesha, Wis. Morry Gash/AP hide caption

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Wisconsin Gov. Scott Walker (R) after his victory Tuesday. Scott Olson/Getty Images hide caption

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Getting out the vote: In Janesville, Wis., on Monday, Democrat Wanda Sonnentag was calling voters. Scott Olson/Getty Images hide caption

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Volunteers at the Wisconsin Democratic Party's recall office in Waukesha entered names from petitions to recall Gov. Scott Walker into their voter databases on March 20. Liz Halloran/NPR hide caption

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