Democratic presidential candidate Bernie Sanders speaks during a rally in Washington, D.C., on June 9. Although he didn't win the nomination, Sanders' grass-roots fundraising has broken records.
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Colorado Democrats pack a gym at a Denver high school during caucuses on March 1, 2016. The crowds and long lines have led to calls for the state to move to an open primary system.
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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.
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.