Democratic presidential hopefuls (from left): Sen. Cory Booker, D-N.J., former Vice President Joe Biden, and Sen. Kamala Harris, D-Calif., onstage before the July debate.
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Democratic presidential candidate Sen. Elizabeth Warren of Massachusetts addresses the Moral Action Congress of the Poor People's Campaign on June 17 in Washington, D.C.
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A worker sweeps the stage prior to the first Democratic presidential debate on April 26, 2007, in Orangeburg, S.C. The debate featured eight Democratic presidential candidates.
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The podiums are seen on the stage during final preparations for Saturday night's Democratic presidential debate between Sen. Bernie Sanders, I-Vt., Hillary Rodham Clinton and former Maryland Gov. Martin O'Malley, in Des Moines, Iowa.
During the 2012 campaign cycle, CNN was among several news networks that hosted Republican debates. Now, the GOP says it doesn't want to be on either that network or NBC.
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