Former Vice President Joe Biden remains the front-runner among the 2020 Democratic presidential hopefuls – despite not officially entering the race – and he performs the best of those potential nominees in a hypothetical matchup with President Donald Trump, according to a Fox News poll released Sunday.

Asked whom they would like to see win the nomination from a list of 20 potential candidates, 31 percent of Democratic primary voters choose Biden. Sen. Bernie Sanders, I-Vt., comes in second with 23 percent, followed by California Sen. Kamala Harris (8 percent), former Texas Rep. Beto O'Rourke (8 percent), Massachusetts Sen. Elizabeth Warren (4 percent) and New Jersey Sen. Cory Booker (4 percent).

Two percent or fewer Democratic primary voters chose each of the other potential candidates. Eleven percent say they don't know whom they would vote for.

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Overall, 67 percent of Democratic primary voters say they would like Biden to enter the race, and 19 percent say they hope he stays out.

Biden performed the best of the potential Democratic nominees in a theoretical head-to-head matchup with Trump. If the election were held today, 47 percent of voters say they would vote for Biden, and 40 percent say they would vote for Trump.

The poll found Sanders winning a contest with Trump, although by a narrower 44 to 41 percent. The other two potential matchups against Trump that pollsters looked at were Warren and Harris. Harris trailed Trump 39-41, and Warren was behind 40-42.

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Beating Trump remains the top criteria for Democrats as they select their standard bearer to try to unseat the president. Thirty-six percent of Democratic primary voters say the candidate they like the most will be the one they support. Fifty-one percent say the more important question is who can defeat Trump.

"Democratic primary voters would welcome Biden into the field, should he run," says Democratic pollster Chris Anderson, who conducted the Fox News Poll with Republican Daron Shaw. "They prioritize beating Trump, and as of now, Biden fares best of the more widely known Democratic candidates against Trump."

The poll was conducted from March 17-20, before the news broke that special counsel Robert Mueller completed his investigation into Russian election meddling without any further indictments.

Fifty-two percent of respondents say they approve of Mueller's handling of the investigation, and 36 percent say they disapprove. Eighty percent say Mueller's report should be made public. Fifty-two percent say Trump tried to interfere in the investigation, and 36 percent say he did not. Forty-five percent say they trust Mueller to tell the truth more than Trump, and 29 percent say they trust Trump over Mueller.

The poll found Trump's approval rating unchanged from 46 percent in February.

The Fox News poll was conducted from a random sample of 1,002 registered voters with a margin of error of plus or minus 3 percentage points.