Voters Cast Ballots In The Wisconsin Presidential Primary Election [Getty Images]

A 'Photo ID Required Today' sign hangs at the entrance of a polling location during the presidential primary vote in Waukesha, Wisconsin, U.S., on Tuesday, April 5, 2016. Wisconsin voters went to the polls Tuesday to decide whether Donald Trump's latest self-inflicted wounds are deep enough to deny him a win in the state's Republican primary, and, in turn, to diminish his hopes of winning the presidential nomination. Photographer: Daniel Acker/Bloomberg via Getty Images

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