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Democratic presidential candidates Senator Bernie Sanders, former Vice President Joe Biden and Senator Elizabeth Warren ap...

How old is too old to be president? 3 oldest Democratic candidates defend ability to do the job

The three oldest candidates in the Democratic presidential field are facing questions over their age during Tuesday night’s debate.

Bernie Sanders is the oldest candidate at 78 and just returned to the campaign trail after suffering a heart attack. He declined to answer when asked how he would reassure Americans of his good health, saying only that he would run a “vigorous campaign all over this country.”

READ MORE: Why New Hampshire could be the jump ball of the 2020 primaries

Seventy-six-year-old Joe Biden argued that his experience and wisdom are assets because “I know what has to be done” as president. He also promised to release his medical records before the first nominating contest in Iowa in February.

And Elizabeth Warren, who’s 70 years old, promised to outwork, out-organize and outlast anyone, including the Republicans.