Former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE leads among 2020 Democratic candidates in early voting states, according to a new CBS poll, with Sens. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.) and Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.) placing second and third, respectively.

Biden is the first choice for 31 percent of voters in 18 early voting states, according to the survey, followed by Warren with 17 percent, Sanders with 16 percent and Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) with 10 percent.

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When Democratic voters are asked which candidate they are considering supporting and allowed to choose as many candidates as they want, Biden still leads with 55 percent, but Warren is closer behind, with 49 percent saying they are considering supporting her.

Harris follows with 45 percent, Sanders with 43 percent and South Bend, Ind. Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE with 32 percent.

In Iowa, Biden still leads, but his competition is closer for voters’ first choice. Biden is the first choice of 30 percent of Democrats in the first-in-the-nation caucus state, followed by Sanders with 22 percent, Warren with 12 percent and Buttigieg with 11 percent.

The breakdown is similar among New Hampshire voters, with Biden at 33 percent, Sanders at 20 percent, Warren at 17 percent and Buttigieg at 10 percent.

In South Carolina, the first primary state in which black voters are a major factor, Biden has a wider lead with 45 percent, followed by Sanders with 18 percent and Warren with 8 percent.

Seventy-five percent of voters supporting Biden believe he would beat President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE in a head-to-head contest.

The survey was conducted by YouGov from May 31 to June 12 among 16,624 registered voters in 18 states. It had a 1.5-point margin of error.