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Joe Biden.
The Delaware Democrat garnered 31% support in the poll, which consisted of interviews with 400 Democratic primary voters between December 6 and 7.
Coming in second was Sen. Bernie Sanders of Vermont - who staged an insurgent 2016 presidential bid - with 24%. Sen. Elizabeth Warren of Massachusetts, with 16%, was third.
No other potential candidate included in the poll garnered more than 4%, and 14% of respondents were undecided.
Biden said recently he would run for the presidency in 2020, but he backed slightly off of that in an interview with the "Late Show" host Stephen Colbert last week.
"I don't plan on running again, but to say you know what's going to happen in four years I just think is not rational," Biden said in the interview.
He added that you can "never say 'never.'"
"Hell, Donald Trump's going to be 74. I'll be 77, in better shape," Biden quipped. "I mean, what the hell?"
Biden opted not to jump into the 2016 race last October after months of mulling over the decision that followed the death of his son, Beau.