Democratic presidential hopefuls (L-R) Former US Vice President Joseph R. Biden Jr., US Senator for Vermont Bernie Sanders and US Senator for California Kamala Harris arrive on stage for the second Democratic primary debate of the 2020 presidential campaign season hosted by NBC News at the Adrienne Arsht Center for the Performing Arts in Miami, Florida, June 27, 2019.

Here are the candidates who qualified for the Houston debate, ordered by their standing in the RealClearPolitics national polling average:

In a primary where national polling has found three contenders separated from the rest of the pack, the debate gives lesser-known candidates a chance to make their case with a national platform. It will also for the first time put frontrunner Joe Biden on the same stage as all of the other top-tier candidates who aim to cut into the former vice president's edge.

ABC News on Thursday unveiled the lineup for the debate set for Sept. 12 in Houston. Unlike the past two debates that featured 20 Democrats over two nights, the next event will see all qualified candidates on one stage.

Only 10 Democrats will take the stage in next month's 2020 presidential primary debate as the jammed field starts to shrink.

Notably, Warren will get her first chance to share a debate stage with Biden. Warren and Sanders have both called for more stark changes to the political and economic system than Biden, who seeks more gradual shifts on health care and climate change, among other issues.

The debate will take place from 8 p.m. ET to 11 p.m. ET on Sept. 12.

To make the debate, Democrats had to get contributions from 130,000 unique donors and hit 2% or more support in four national or early state polls. A couple of candidates fell just short: billionaire activist Tom Steyer needed only one more qualifying poll, while Rep. Tulsi Gabbard, D-Hawaii, needed two more.

Democrats have hammered the Democratic National Committee over the debate qualification process. As Steyer came close to getting on the stage, some rivals argued the former hedge fund manager used his vast wealth to blanket early states with ads and effectively buy support.

Others asserted the DNC aimed to block candidates who failed to crack the top tier in the field of more than 20 candidates. Some candidates could still qualify for the fourth debate even if they did not make the stage in Houston.

Several Democrats who failed to gain traction in the primary dropped out in recent weeks as it became clear they would not qualify for the debate.

Sen. Kirsten Gillibrand, D-N.Y., left the race on Wednesday. Former Colorado Gov. John Hickenlooper, Washington Gov. Jay Inslee, Rep. Seth Moulton, D-Mass., and Rep. Eric Swalwell, D-Calif., have also scrapped their White House bids.

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