WASHINGTON – Sen. Bernie Sanders finished ahead of Joe Biden in the first major national poll of the year that did not find the former vice president leading the pack of potential 2020 Democratic presidential candidates.

When asked whom they would support from a list of 20 candidates – including "someone else" – 29% named Sanders, and 24% named Biden in an Emerson College poll released Monday. They were trailed by South Bend, Indiana, Mayor Pete Buttigieg, who was the pick of 9% of likely Democratic primary voters.

California Sen. Kamala Harris and former Texas Rep. Beto O'Rourke each came in at 8%, and 7% picked Massachusetts Sen. Elizabeth Warren. Former Housing and Urban Development Secretary Julián Castro got 3%, as did entrepreneur Andrew Yang. New Jersey Sen. Cory Booker got 2%, and the rest of the field got 1% or less.

The full field of candidates:Who is running for president in 2020?

Money primary:Celebrities back Harris in 2020 fundraising, MAGA hats power Trump's haul in FEC reports

"Biden has seen his support drop. In February, he led Sanders 27% to 17%, and in March, the two were tied at 26%. Now, Sanders has a 5-point lead," said Spencer Kimball, director of Emerson Polling.

"While still early in the nominating process, it looks like Mayor Pete (Buttigieg) is the candidate capturing voters’ imagination; the numbers had him at 0% in mid-February, 3% in March and now at 9% in April," Kimball noted.

The survey is the first of more than three dozen 2020 polls listed by RealClearPolitics dating back to October to show Sanders ahead of Biden, including the Emerson poll in March in which they tied.

In December, a poll by McLaughlin & Associates found Sanders with a 1-point lead, but RealClearPolitics does not include results from that firm.

The latest poll from Morning Consult – which posts updates on the 2020 Democratic race every week – indicates the Emerson result could be an outlier. Its survey, based on 12,550 interviews conducted from April 8-14, found Biden with 31% support among Democratic primary voters and Sanders with 23%. Harris finished third at 9%, followed by O'Rourke with 8% and Buttigieg with 7%.

The RealClearPolitics polling average shows Biden with a 9.3-percentage-point lead over Sanders.

In a head-to-head matchup with President Donald Trump, Biden still performed the best in the Emerson poll, leading the incumbent 53% to 47%. But that was a slide from the college's poll in March in which he topped Trump 55% to 45%.

Sanders edged out Trump 51% to 48%, and Harris tied him in a hypothetical matchup. The rest of the Democratic field trailed Trump, who had a 43% approval rating among respondents.

Trump leads former Massachusetts Gov. William Weld – who is his only challenger for the nomination – 85% to 15% among Republican primary voters.

The Emerson poll was conducted April 11-14 with a margin of error of plus or minus 5.2 percentage points.

Bernie Sanders:Vermont senator appears at Fox News town hall and survives. Who's next? Anyone?

More:Bernie Sanders releases 10 years of long-anticipated taxes