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Republican Presidential hopeful Donald Trump speaks as Ben Carson looks on during in the CNBC Republican Presidential Debate, October 28, 2015 at the Coors Event Center at the University of Colorado in Boulder, Colorado. AFP PHOTO/ ROBYN BECK        (Photo credit should read ROBYN BECK/AFP/Getty Images)
Republican Presidential hopeful Donald Trump speaks as Ben Carson looks on during in the CNBC Republican Presidential Debate, October 28, 2015 at the Coors Event Center at the University of Colorado in Boulder, Colorado. AFP PHOTO/ ROBYN BECK        (Photo credit should read ROBYN BECK/AFP/Getty Images)

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    Trump goes after Carson ahead of debate

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Trump goes after Carson ahead of debate

As polls show the neck-and-neck, Donald Trump is calling out Ben Carson for an unconventional campaign. CNN's Dana Bash reports.

Trump goes after Carson ahead of debate

As polls show the neck-and-neck, Donald Trump is calling out Ben Carson for an unconventional campaign. CNN's Dana Bash reports.