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ALEXANDRIA, UNITED STATES - OCTOBER 16: Republican presidential candidate Dr. Ben Carson answers questions from members of the press after delivering brief remarks to supporters at the King Street Retail Walk October 16, 2015 in Alexandria, Virginia. Carson discussed threats facing the United States during his remarks. (Photo by Win McNamee/Getty Images)

ALEXANDRIA, UNITED STATES – OCTOBER 16: Republican presidential candidate Dr. Ben Carson answers questions from members of the press after delivering brief remarks to supporters at the King Street Retail Walk October 16, 2015 in Alexandria, Virginia. Carson discussed threats facing the United States during his remarks. (Photo by Win McNamee/Getty Images)