Republican presidential candidate Donald Trump smiles following his victory in the May 3 Indiana primary, which cemented his status as the GOP's de facto nominee.
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Democratic presidential candidate Bernie Sanders addresses a rally Wednesday at the Santa Clara County Fairgrounds in San Jose, Calif. The senator's campaign is intently focused on a big win in the state on June 7, and has poured money into TV ads there.
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Democratic presidential candidate Hillary Clinton talks with Bo Copley, who recently lost his job at a coal company, at a campaign roundtable in West Virginia on May 2, 2016.
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.