Conservative donor David Koch in a 2013 file photo. The political network he and his brother, Charles, have created is not backing Donald Trump's presidential bid this year.
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Donald Trump began his campaign for president saying he would pay for it out of his own pocket. Now, he is accepting big donations and has a superPAC working on his behalf.
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Republican presidential candidate Donald Trump in Dallas on June 16, 2016. Trump's campaign is struggling to raise money to finance his bid against Democrat Hillary Clinton.
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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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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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