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Voters take to the polls in Arizona and Michigan

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A shadow of a man falls on a pillar of the Wickenburg Community Center as he enters the polling place to vote on Feb. 28 in Wickenburg, Ariz.

Evan Vucci / AP

Molly Clemmons, 6, Likeigh Barcomb, 5, and Katie Clemmons, 2, talk with Ray Battle before a rally for Republican presidential candidate Newt Gingrich on Feb. 28 in Rome, Ga.

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Republican presidential candidate Rick Santorum calls potential voters under the watchful eyes of reporters during a visit to his campaign office on Feb. 28, 2012 in Grand Rapids, Mich.

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Children watch as Republican presidential candidate and former Massachussetts Gov. Mitt Romney speaks during a press availability following a visit to his Michigan campaign headquarters on Feb. 28 in Livonia, Mich.

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John Vandermark wears his "I Voted" sticker after voting on primary day on Feb. 28, in Royal Oak, Mich.

Republican rivals Mitt Romney and Rick Santorum collided Tuesday in a rancorous Michigan presidential primary that tested the clout of the GOP establishment against conservative and tea party rebels as well as the candidates themselves. Arizona Republicans voted in the second primary of the night, and Romney was favored by far in that race that drew less attention.

-- The Associated Press contributed to this post

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