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DES MOINES, IA - AUGUST 16:  Republican presidential hopeful Ben Carson speaks during the Iowa State Fair on August 16, 2015 in Des Moines, Iowa.  Presidential candidates are addressing attendees at the Iowa State Fair on the Des Moines Register Presidential Soapbox stage and touring the fairgrounds. The State Fair runs through August 23.  (Photo by Justin Sullivan/Getty Images)
DES MOINES, IA - AUGUST 16:  Republican presidential hopeful Ben Carson speaks during the Iowa State Fair on August 16, 2015 in Des Moines, Iowa.  Presidential candidates are addressing attendees at the Iowa State Fair on the Des Moines Register Presidential Soapbox stage and touring the fairgrounds. The State Fair runs through August 23.  (Photo by Justin Sullivan/Getty Images)

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    Ben Carson continuing to climb in GOP polls

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Ben Carson continuing to climb in GOP polls

As Republican presidential candidate Dr. Ben Carson continues to rise in the polls, frontrunner Donald Trump continues to exchange barbs with Governor Jeb Bush. CNN's Dana Bash reports.

Ben Carson continuing to climb in GOP polls

As Republican presidential candidate Dr. Ben Carson continues to rise in the polls, frontrunner Donald Trump continues to exchange barbs with Governor Jeb Bush. CNN's Dana Bash reports.