Former Vice President Joe Biden leads his closest challenger in the 2020 Democratic presidential field, Sen. Bernie Sanders (I-Vt.), by 6 percentage points, according to a poll released Thursday by CNN.

The poll found Biden with the support of 26 percent of Democratic primary voters surveyed, followed by Sanders with 20 percent. Sen. Elizabeth Warren (D-Mass.) came in third with 16 percent, followed by South Bend, Ind., Mayor Pete Buttigieg at 8 percent and former New York City Mayor Michael Bloomberg at 5 percent. Entrepreneur Andrew Yang and Sens. Amy Klobuchar (D-Minn.) and Cory Booker (D-N.J.) are tied at 3 percent each, according to the survey.

CNN noted that Biden led the same poll with 33 percent support about a year ago, but has dipped since then, while Sanders has risen in the same period from 14 percent. Warren had 4 percent last December, the network added.

Pollsters also found satisfaction with the Democratic field has decreased since June, when 38 percent of respondents said they were "very satisfied," compared to 31 percent in the latest survey.

The survey also found increased enthusiasm among voters, with half of registered voters now saying they are very enthusiastic about voting for president in 2020, an all-time high since CNN began polling the question in 2003. Enthusiasm among Democrats has increased from 46 percent to 58 percent in a month, while Republican enthusiasm increased 7 points to 59 percent.

The poll also found a reduced percentage of Democratic voters - now 47 percent - who say their top priority is a candidate's capacity to beat President Trump compared to their stances on political issues. Eleven percent said electability and positions are of equal importance, another all-time high.

Forty percent say they consider Biden to be the candidate best positioned to beat Trump, followed by Sanders, who 16 percent said was best. On the question of political issues, 28 percent said Sanders agrees with their views on important issues, followed by 19 percent who chose Biden.

SSRS conducted the poll from Dec. 12-15 among a random national survey of 1,005 adults, including 408 registered Democrats or Democratic-leaning independents. It has a margin of error of 3.7 percentage points.