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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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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Sen. Bernie Sanders waves to a crowd gathered at Gettysburg College in Gettysburg, Pa., on Friday. Pennsylvania holds its presidential primary Tuesday. Mark Wilson/Getty Images hide caption

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Sanders Adviser Says Campaign May Have To 'Re-Evaluate' After Tuesday
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