Almost one-third of registered Democratic voters back former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE for the party’s 2020 presidential nomination, making him the front-runner in a new poll provided exclusively to The Hill.

Biden is the clear leader in Harvard CAPS/Harris’s June poll with support from 32 percent of Democrats polled. Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE, the party’s 2016 nominee, finished second with 18 percent of the vote, while her 2016 primary opponent, Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), sits in third with 16 percent.

Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) was the only other candidate to poll in double digits, with 10 percent of those surveyed backing her.

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Biden has spoken frankly about both his interest in running for president and his hesitancy to jump in the race.

He flirted with a bid in 2016 but ultimately decided not to run while he mourned the death of his son, Beau. This week, he joked to The Washington Post that he isn’t “looking to live in the White House,” but added, “I don’t know what I’m going to do.”

Another Clinton bid is seen as far less likely than possible bids by Sanders and Warren, who have been crisscrossing the country and heavily fundraising.

The Harvard/Harris poll also tests the 2020 chances of Sens. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.), Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.) and Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.), as well as billionaire Michael Bloomberg and New York Gov. Andrew Cuomo (D).

In that group, Booker fares best among respondents with 6 percent of them backing him, followed by Bloomberg’s 3 percent and Harris’s 2 percent. Cuomo and Gillibrand were each backed by 1 percent of those surveyed, while 12 percent said they supported someone not listed.

Unlike the 2016 field, which had been viewed as a one-person race until Sanders’s surprising rise, the 2020 Democratic primary race appears to be wide open and is expected to attract more than a dozen hopefuls.