Republican presidential nominee Donald Trump and Democratic presidential nominee Hillary Clinton are introduced at the start of Monday night's presidential debate at Hofstra University in Hempstead, N.Y.
Left: Republican nominee Donald Trump speaks during the presidential debate at Hofstra University on Monday in Hempstead, N.Y. Right: Democratic nominee Hillary Clinton speaks during the debate.
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Republican presidential nominee Donald Trump speaks as Democratic presidential nominee Hillary Clinton and moderator Lester Holt listen during Monday night's presidential debate at Hofstra University in Hempstead, N.Y.
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Then-presidential candidate Rick Santorum speaks to reporters in the spin room Jan. 14 after the undercard portion of the Fox Business Network Republican presidential debate in South Carolina.
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Republican presidential candidate Donald Trump and Fox News Channel host and moderator Megyn Kelly during the first Republican presidential debate — the origin of their feud.
Donald Trump (left) and Ted Cruz joke about Trump's comments that Cruz was a "maniac" and didn't have the right temperament to be president. They played nice then, but will they again?
Democratic presidential candidates Bernie Sanders, Hillary Clinton and Martin O'Malley stand on the stage prior to Saturday's Democratic primary presidential debate in Des Moines, Iowa.
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Republican presidential candidates, from left, Bobby Jindal, Rick Santorum, George Pataki, and Lindsey Graham take the stage during the CNBC Republican presidential debate at the University of Colorado on Wednesday.
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Sen. Marco Rubio, R-Fla., left, and Ben Carson have surged ahead of other GOP candidates, like former Florida Gov. Jeb Bush, to take center stage with Donald Trump at next week's GOP debate.