A supporter of Democratic presidential candidate Hillary Clinton wears campaign buttons as she listens to former President Bill Clinton at an event in Indiana. Joe Raedle/Getty Images hide caption

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Vice President Hubert Humphrey (right) and his running mate, Sen. Edmund S. Muskie, wave to the crowd with their wives at the Democratic Convention in Chicago on Aug. 29, 1968. Violence ensued inside and outside the convention hall. AP hide caption

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Bernie Sanders addresses supporters on Coney Island Boardwalk ahead of the April 19 New York primary. Pacific Press/LightRocket via Getty Images hide caption

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After String Of Losses, Sanders Campaign To Lay Off 'Hundreds' Of Staffers
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Republican presidential candidate Sen. Ted Cruz is joined by former Hewlett-Packard CEO Carly Fiorina during a rally in Indianapolis on Wednesday. Cruz announced he has tapped Fiorina to serve as his running mate. Michael Conroy/AP hide caption

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Hillary Clinton addresses supporters after winning four of five Northeastern states Tuesday night. Eduardo Munoz Alvarez/AFP/Getty Images hide caption

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Republican presidential candidate Donald Trump speaks at a campaign rally Monday in Wilkes-Barre, Pa. Trump won Tuesday's primary race in the state Mel Evans/AP hide caption

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