Former Arkansas Gov. Mike Huckabee speaks at the Republican National Convention Wednesday. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

Sen. Bill Frist (left) gives a mock smallpox vaccine during a training session in 2003. Frist, a surgeon, once gave CPR to a visitor who collapsed in a Senate office building. Susan Walsh/AP hide caption

itoggle caption Susan Walsh/AP

Former Massachusetts Gov. Mitt Romney speaks to the Values Voter Summit, held by the Family Research Council Action, Friday, Sept. 17, 2010, in Washington.  Jacquelyn Martin/Associated Press hide caption

itoggle caption Jacquelyn Martin/Associated Press