Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE are running neck and neck in the 2020 Democratic primary, a new Quinnipiac University poll released Tuesday showed.

Twenty-nine percent of Democratic voters and independent voters who lean Democratic said they support Warren, while Biden received 26 percent support from the same group, a difference within the poll’s margin of error.

Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) came in third with 16 percent, while no other candidate broke double digits.

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The three candidates had similar showings in a September Quinnipiac University poll, which saw Warren, Biden and Sanders at 27 percent, 25 percent and 16 percent, respectively.

“Warren maintains her strength in the Democratic primary, which has been consistently growing since the start of her campaign. This poll confirms her status as a co-frontrunner with Biden,” said Quinnipiac University Polling Analyst Tim Malloy.

Warren leads all other candidates in the poll among both male and female voters as well as white voters and voters with a college degree. Biden leads among black voters, voters without a college degree, and voters aged 65 years and older.

Sanders continues to show strength among younger voters, reaching a 22-point edge among those aged 18 to 34. Sanders's consistency in his overall support suggests that news he suffered a heart attack did not substantially impact his backing.

Tuesday’s survey matches similar polling that has signaled a cleavage within the primary field, with Warren, Biden and Sanders making up its top tier while relegating other high-profile candidates such as Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.) 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 to its middle tier.

Biden has maintained a narrowing lead over Warren and Sanders in most national and statewide polls, largely on the strength of his deep well of support among African Americans.

But Warren has surpassed Biden in recent weeks in a handful of surveys, with polls showing her slowly closing the gap among black voters.

The Quinnipiac University poll surveyed 646 Democratic voters and independent voters who lean Democratic from Oct. 4 to Oct. 7 and has a margin of error of 4.7 percentage points.