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LAS VEGAS, NV - DECEMBER 14:  Republican presidential candidate Donald Trump speaks during a campaign rally at the Westgate Las Vegas Resort & Casino on December 14, 2015 in Las Vegas, Nevada. Donlad Trump is campaigning in Las Vegas a day ahead of the final GOP debate.  (Photo by Justin Sullivan/Getty Images)
LAS VEGAS, NV - DECEMBER 14:  Republican presidential candidate Donald Trump speaks during a campaign rally at the Westgate Las Vegas Resort & Casino on December 14, 2015 in Las Vegas, Nevada. Donlad Trump is campaigning in Las Vegas a day ahead of the final GOP debate.  (Photo by Justin Sullivan/Getty Images)

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    How Donald Trump proved critics wrong in 2015

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How Donald Trump proved critics wrong in 2015

Donald Trump defied the critics in 2015 using fiery rhetoric to come out of nowhere to lead the Republican presidential field. CNN's Tom Foreman reports.

How Donald Trump proved critics wrong in 2015

Donald Trump defied the critics in 2015 using fiery rhetoric to come out of nowhere to lead the Republican presidential field. CNN's Tom Foreman reports.