Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, left, waves as Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, center, and Martin OMalley, former governor of Maryland and 2016 Democratic presidential candidate, look on during candidate introductions at the Jefferson-Jackson Dinner in Des Moines, Iowa, U.S., on Saturday, Oct. 24, 2015. With Vice President Joe Biden officially out of the presidential race, the nation's first nominating contest between front-runner Clinton and Sanders is gaining steam, according to a new Bloomberg Politics/Des Moines Register Iowa Poll. Photographer: Daniel Acker/Bloomberg via Getty Images
