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Republican presidential candidates, from left, Donald Trump, Carly Fiorina, Ted Cruz, Jeb Bush, and Ben Carson leave the stage following the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015, in Las Vegas (Credit: AP Photo/John Locher)

Republican presidential candidates, from left, Donald Trump, Carly Fiorina, Ted Cruz, Jeb Bush, and Ben Carson leave the stage following the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015, in Las Vegas (Credit: AP Photo/John Locher)