In a 1988 debate against George H.W. Bush, Michael Dukakis's answer to a question about whether he would support the death penalty if his wife were raped and murdered is considered a huge stumble. LENNOX MCLENDON/ASSOCIATED PRESS hide caption

itoggle caption LENNOX MCLENDON/ASSOCIATED PRESS

Hillary Clinton's "inevitability" became less certain after a debate in Philadelphia at Drexel University in October 2007. William Thomas Cain/Getty Images hide caption

itoggle caption William Thomas Cain/Getty Images