A new 2020 Democratic primary poll from ABC News and The Washington Post found a slight dip in former Vice President Joe Biden's and Sen. Bernie Sanders' numbers, with Biden still in the lead, with 27% support, and Sanders as runner-up, with 19%.

Sen. Elizabeth Warren came in third with 17% support, up 6 points from the previous poll by ABC News and The Post.

Sen. Kamala Harris saw a slump to 7% support, down 4 points from the July 1 poll. Mayor Pete Buttigieg maintained a steady 4% support.

ABC News is a cosponsor along with Univision of the next Democratic debate, set to take place in Houston on Thursday.

Visit Business Insider's homepage for more stories.

ABC News, the cosponsor of Thursday night's scheduled Democratic presidential primary debate in Houston, has released a new poll measuring candidate support among Democrats and Democratic-leaning independents. It found former Vice President Joe Biden in the lead with 27% support, followed by Sens. Bernie Sanders and Elizabeth Warren at 19% and 17%, respectively. Other candidates trailed by 10 percentage points or more.

Produced by Langer Research Associates for ABC News and The Washington Post, the poll compared preferences on September 2-5 with those from early July, days after the first 2020 Democratic debates. It surveyed 1,003 adults by phone, of whom 437 said they leaned Democratic and were asked about the primary race.

Both Biden and Sanders saw slight slumps from the July poll, with Biden losing 2 percentage points and Sanders losing 4.

Warren's numbers increased by a striking 6 points, the only candidate to gain a percentage. Sen. Kamala Harris fell to 7% support from 11%, and Mayor Pete Buttigieg remained steady with an unchanged 4%. Former Rep. Beto O'Rourke and the entrepreneur Andrew Yang received 3% support, and all other candidates fell under 1%.

Ten candidates are set to take the stage Thursday for the third round of Democratic primary debates, sponsored by ABC News and Univision.

Candidates in Detroit for the second round of Democratic presidential debates. Associated Press

Read more: POWER RANKING: Here's who has the best chance of becoming the 2020 Democratic presidential nominee

ABC News noted that Sen. Amy Klobuchar and Rep. Tulsi Gabbard saw their support double to 2% among registered voters, while Biden and Warren gained 2 points and 1 point among such respondents.

According to the poll, Warren's gains were in the Northeast, where the Massachusetts senator is from, in urban areas, and among liberals. Harris lost 10 points among seniors, who lean toward Biden. But a full 55% of the Democratic-leaning respondents said they would consider switching their candidate preference.

Biden was the only candidate for whom a majority of current supporters pledged to see their support through to the primary. Sixty-four percent said they'd definitely support him, as compared with 34% of committed voters for all the other Democratic candidates combined. Biden also reigned supreme as the candidate Democratic-leaning respondents thought had the best chance of beating President Donald Trump, with 42% picking him as the most likely to win in a general election, compared with 14% for Sanders and 12% for Warren.

But while primary polls have historically been good predictors, even this early out, general-election polls are not. Being able to beat Trump was important to a majority of Biden and Warren supporters, whereas Sanders supporters ranked "closest to me on issues" as more important. When asked whether Biden was "the best president for the country," his numbers dropped to 23%, with Warren at 19% and Sanders at 16%.

Biden's support in the past two ABC/Post polls has stemmed largely from black voters, who ABC News said favored him at 44%, double his support from white and Hispanic voters. He also led among moderates in the latest poll with 33% support but had comparable numbers to Sanders and Warren among liberals. In terms of age, Biden has courted seniors, whereas 41% of voters ages 18 to 29 in the latest poll preferred Sanders.