U.S. Rep. Beto O'Rourke speaks during a campaign rally in Plano, Texas, on Saturday. O'Rourke is the Democratic challenger for the Senate seat currently held by Senator Ted Cruz, R-Texas.
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Former President Bill Clinton plays with balloons onstage at the end of the fourth day of the Democratic National Convention at the Wells Fargo Center in Philadelphia in July.
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Indiana Gov. Mike Pence, the Republican vice presidential nominee, headlined Wednesday's event. But all eyes were on Ted Cruz earlier in the evening for his refusal to endorse Donald Trump.
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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.