Democratic presidential debate in Iowa

Democratic presidential candidates Bernie Sanders, left, Hillary Rodham Clinton and Martin O’Malley participate in a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Bernie Sanders, left, makes a point as Hillary Rodham Clinton listens during a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Bernie Sanders speaks during a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Hillary Rodham Clinton waves as Bernie Sanders, left, and Martin O’Malley prepare before a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Democratic presidential candidates Hillary Rodham Clinton, Bernie Sanders and Martin O’Malley take the stage during a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Martin O’Malley, right, speaks as Hillary Rodham Clinton watches during a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.

Hillary Rodham Clinton speaks during a Democratic presidential primary debate, Saturday, Nov. 14, 2015, in Des Moines, Iowa.