Here are a few things to watch:
Biden under siege?
The slimmed-down field will boast eight progressives who will surround and outnumber the two more moderate candidates on the stage: Former Vice President Joe Biden and U.S. Sen. Amy Klobuchar.
Biden, the front-runner in polls, will be at the center of the debate and how he responds to attacks from will shape the three-hour event.
He’s faced increasing scrutiny over a string of gaffes in recent weeks, but he’s also been more willing to aggressively defend his record and highlight contrasts with opponents on health care, criminal justice policy and the legacy of President Barack Obama.
Heightening the drama will be his placement on the stage: He’ll be sandwiched in between the party’s two biggest liberal stars, who also are his closest rivals in the polls: U.S. Sens. Bernie Sanders and Elizabeth Warren.
How will Warren position herself?
The Democratic presidential hopefuls have met twice before, but Thursday will be the first time that Biden and Warren share the same stage.
It will be a clash of competing ideologies and approaches to the campaign: She advocates for “big structural change” and has honed a reputation for wonkish, detailed plans. He tends to speak in broader strokes, and argues that the electorate is more willing to back a centrist candidate than it seems.
The most notable divide could come over health care. Biden supports a public option but doesn’t back eliminating private insurance. The latter part is a key part of Warren’s “Medicare for all” plan.
A test for the liberal alliance
Sanders and Warren have avoided any significant showdown this year, with each trading glowing words about their long friendship, but their alliance will face a major test at Thursday’s debate.
But with polling numbers beginning to gel, the two will face new pressure to draw contrasts on policy and approach.
And they could also face new challenges from other liberals, including U.S. Sens. Cory Booker and Kamala Harris, who are trying to win over black supporters who have embraced Warren.
Will the second-tier step up?
Several candidates who failed to gain traction or fundraising momentum have abandoned the White House race since the last debate, including U.S. Sen. Kristen Gillibrand and former Colorado Gov. John Hickenlooper.
That raises the pressure on the remaining second-tier candidates.
For a time, it seemed Harris would join the frontrunners, particularly after a breakout moment during the first debate when the California senator’s criticism of Biden’s record on race and busing left him struggling to respond.
But her poll numbers have dipped since then, and other candidates – including South Bend, Ind. Mayor Pete Buttigieg and former U.S. Rep. Beto O’Rourke – have failed to capitalize on strong fundraising and a sense of early momentum.
Who is in the debate:
Sen. Cory Booker, of New Jersey
Former Vice President Joe Biden
Mayor Pete Buttigieg, of South Bend, Indiana
Julián Castro, the former housing secretary
Sen. Kamala, Harris of California
Sen. Amy Klobuchar, of Minnesota
Former Rep, Beto O’Rourke, of Texas
Sen. Bernie Sanders, of Vermont
Sen. Elizabeth Warren, of Massachusetts
Andrew Yang, a tech entrepreneur
How to watch the debate:
The debate will air on ABC from 8 to 11 p.m. ET. It will be held at Texas Southern University, a public historically black university in Houston.
Here is the livestream from ABC News: