Registered Democrats were asked in the Reuters-Ipsos survey who they would back in the primary election if it were held today.
Bernie Sanders and Joe Biden were tied at 21%.
A new poll found that 40 percent of Democrats thought the ability to beat Trump was the "most important character trait." Biden was considered to be best candidate to beat Trump, with 35% of Democrat respondents thinking he could win.
Sanders polled at just 15% electability.