With Elizabeth Warren challenging Joe Biden for the front-runner label, the backdrop to Tuesday night’s Democratic presidential debate is significantly different from prior matchups.

What’s more, Bernie Sanders is facing questions about his ability to go the distance as he recovers from a heart attack this month, and the clash in Ohio will be the first debate since House Democrats launched their official impeachment inquiry into President Donald Trump.

In addition, two long-shot candidates, Hawaii Rep. Tulsi Gabbard and hedge-fund billionaire Tom Steyer, are slated to get spots on the debate stage after failing to qualify for last month’s clash. That has raised the total number of invited contenders from 10 to a dozen.

The debate, run by AT&T’s T, CNN and the New York Times NYT, +0.19% , is due to start at 8 p.m. Eastern time on Tuesday at Otterbein University in Westerville, a northeastern suburb of Columbus. It’s set to break the record for the number of candidates appearing on a stage at once, topping the prior mark of 11 that was notched by a Republican debate in 2015.

Warren, the progressive Massachusetts senator, may be seeking to reassure her critics during the debate, said Mitchell McKinney, a professor of political communication at the University of Missouri. McKinney said Warren’s message may boil down to the following: “You can commit to me. I am a safe candidate. I will be a strong candidate. Let’s rethink your notions of the safe candidate.”

While Warren edged past Biden in a widely followed average of polls last week, some centrist Democrats continue to worry about her policy plans that target Wall Street and other sectors. Party fundraisers “think Warren can’t win the presidency — and they know she represents a real threat to their companies and their tax rates,” said Greg Valliere, chief U.S. policy strategist at AGF Investments, in a recent note.

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Mizzou’s McKinney said Warren will have to be careful in terms of going directly after Biden, given how Democrats felt about attacks on him in prior debates by California Sen. Kamala Harris and Julián Castro, the former Housing and Urban Development secretary. The Massachusetts lawmaker also will have to take care in how she interacts with Sanders, as she wants to avoid looking like she’s aiming to “kick him when he’s down,” McKinney added.

For Biden, one key will be to “demonstrate to voters that he’s vigorously able to take it to Donald Trump” and also “stand up for himself, his family,” McKinney said. Republicans have emphasized the former vice president’s link to the impeachment effort, which was announced on Sept. 24 and is centered on how Trump asked his Ukrainian counterpart to investigate Biden and his son.

Read more:Ukraine reviews probe into company whose board included Biden’s son

Meanwhile, the 78-year-old Sanders faces a “crucial moment” following his Oct. 1 heart attack, according to McKinney. “If he’s able to turn in a performance that shows us he hasn’t missed a beat, so to speak, that he’s the same old Bernie Sanders — aggressive, passionate — then that will go far to allay questions and fears that maybe he doesn’t have what it takes to run the course,” said the professor, an expert on presidential debates.

The Vermont senator made an effort Monday to act true to form, as his campaign unveiled a plan that promises to “put an end to the corporate greed ruining our country.” His proposal calls for giving workers 20% of their companies’ shares and 45% of their firms’ board seats, and it also would ban large-scale stock buybacks, return the federal corporate tax rate to 35% from 21% and require companies to give stock to workers who lose their jobs due to outsourcing or automation.

Opinion:Sanders and Biden are too old to be president — and so is Trump

And read:Sanders unveils plan targeting money in politics as concerns grow over his heart attack

This CNN graphic shows how candidates will be arranged Tuesday on the debate stage. CNN

The dozen Democrats who have qualified for Tuesday’s debate are Biden, Warren, Sanders, Harris, Castro, Gabbard and Steyer, as well as South Bend, Ind., Mayor Pete Buttigieg; entrepreneur Andrew Yang; former Rep. Beto O’Rourke of Texas; Sen. Cory Booker of New Jersey; and Sen. Amy Klobuchar of Minnesota.

In a RealClearPolitics moving average of polls on Tuesday, Biden had regained front-runner status, scoring 29.4% support vs. Warren’s 23.4%. Sanders drew 15.6% support, topping Buttigieg and Harris at 5.2% each, O’Rourke at 2.6% and Yang at 2.4%. All other Democratic candidates hoping to challenge Trump in November 2020 are below 2%. Ahead of the Sept. 12 debate, Biden was drawing support of 27% vs. 17% each for Warren and Sanders.

Related:Some 2020 Democrats are angling for the vice president slot — a gambit that rarely pays off

And read:19 Democrats are running for president, after more exits from the race

While Gabbard and Steyer have made the cut for the debate, each faces a tricky path, according to McKinney. Gabbard, who took part in June’s and July’s primary debates, threatened to boycott Tuesday’s event, saying the Democratic National Committee and media are trying to “rig the 2020 primary,” but then tweeted Monday that she would be there. Gabbard may be anticipating that she won’t qualify for next month’s debate, the University of Missouri professor said. And Steyer, who is appearing in a 2020 debate for the first time, likely holds minimal appeal to the many Democratic voters who don’t want to see another wealthy businessman with no political experience move into the White House, McKinney added.

To qualify for the fifth primary debate in November, candidates will need to have at least 165,000 unique donors, as well as hit 3% support in at least four national or early state polls — or 5% in two early-state polls. That’s up from the previously required 130,000 donors and 2% support.

Now read:Warren tops Biden in third-quarter fundraising, but both lag Sanders

This is an updated version of a report that was first published on Oct. 12, 2019.