As of the new year, there are four leading contenders for the Democratic presidential nomination, from left: Vermont Sen. Bernie Sanders, former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren and former South Bend, Indiana, Mayor Pete Buttigieg.

As of the new year, there are four leading contenders for the Democratic presidential nomination, from left: Vermont Sen. Bernie Sanders, former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren and former South Bend, Indiana, Mayor Pete Buttigieg.