Democratic presidential candidate Sen. Bernie Sanders, center, speaks as fellow candidates businessman Tom Steyer, from left, Sen. Elizabeth Warren, former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg and Sen. Amy Klobuchar, listen on Jan. 14, during a Democratic presidential debate hosted by CNN and The Des Moines Register.

Democratic presidential candidate Sen. Bernie Sanders, center, speaks as fellow candidates businessman Tom Steyer, from left, Sen. Elizabeth Warren, former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg and Sen. Amy Klobuchar, listen on Jan. 14, during a Democratic presidential debate hosted by CNN and The Des Moines Register.