When 20 Democratic presidential candidates gather for the second round of debates on Tuesday and Wednesday, about half of them will do so with the understanding that it will probably be their last time debating on the national stage this election cycle.
The two debates, which will air on CNN from 8 p.m. until roughly 10:30 p.m. each night, are expected to be more contentious than the first set of debates in Miami last month, when Senator Kamala Harris of California and former Housing Secretary Julián Castro won plaudits and fund-raising boosts with effective attacks against onstage opponents.
Short of a breakout moment that turbocharges their grass-roots fund-raising and juices their support in public polling, half the field is in danger of missing the Democratic National Committee’s qualifying threshold for the next round of debates, scheduled for September.
Officials involved in the campaigns and some of the candidates themselves have foreshadowed testier exchanges this week, as 10 candidates take the stage each night knowing they are fighting for their political lives.
And indeed the debate lineups, chosen during a game show-style live draw on CNN, will provide ample opportunity for rhetorical fireworks.
Tuesday’s debate will place the race’s two liberal front-runners, Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont, together at center stage.
Wednesday’s debate will feature former Vice President Joseph R. Biden Jr., under attack for his past positions on race-related issues, standing between the two leading black candidates: Senators Kamala Harris of California and Cory Booker of New Jersey. Mr. Biden has spent the last month clashing with both.
The candidates will appear at the Fox Theater in downtown Detroit, a venue that hosted the infamous 2016 Republican presidential primary debate in which Donald J. Trump defended the size of his manhood after Senator Marco Rubio of Florida attacked it.
The debates will begin with 60-second opening statements, followed by 60-second responses to questions posed by CNN’s moderators, Dana Bash, Don Lemon and Jake Tapper.
CNN will not ask the candidates “show of hands” questions. And representatives from the network have told the campaigns they will penalize any candidate who “consistently interrupts” by reducing the amount of time that candidate has to speak.
On the first night, CNN’s moderators will undoubtedly seek to draw distinctions between Mr. Sanders and Ms. Warren. Others onstage will also seek to contrast themselves with the race’s leading progressives. Former Gov. John Hickenlooper of Colorado and former Representative John Delaney of Maryland oppose socialism and have attacked Mr. Sanders, a democratic socialist, without much success. Gov. Steve Bullock of Montana, who did not qualify for the first debate in June, has said since then that he would not support extending federal health care benefits to undocumented immigrants, separating himself from most of the presidential field.
Other prospective sources of tension might include a battle between Mayor Pete Buttigieg of South Bend, Ind., and former Representative Beto O’Rourke of Texas — a conflict Mr. O’Rourke’s allies have foreshadowed in recent days. Senator Amy Klobuchar of Minnesota has barely hid her disdain for Mr. Buttigieg and Mr. O’Rourke, two men who are younger and less accomplished than her but have received far more attention in the race. And Marianne Williamson, a self-help author, remains a wild card.
While all 10 candidates debating on Tuesday are white, Wednesday’s debate will feature five people of color, including Ms. Harris and Mr. Booker, who have each placed their bets on wresting the support of black voters away from Mr. Biden.
There’s little doubt Mr. Biden’s record on race will be a focus. Ms. Harris’s broadside during the first debate against Mr. Biden’s decades-old position on mandatory busing to integrate public schools energized her campaign, while Mr. Booker last week hit Mr. Biden for writing the 1994 crime bill, previewing a line of attack.
Mr. Biden’s advisers have said he will be more prepared to fight back Wednesday than he had been in Miami. His aides pre-emptively criticized Mr. Booker last week, highlighting his tenure as the mayor of Newark.
On the stage’s edge, Mr. Inslee is expected to stress his signature issue, climate change, while Ms. Gillibrand may return to a vague attack she launched last week in Iowa, when she accused unnamed presidential rivals of not wanting to see women working “outside the home.”
For candidates like Mr. Inslee and Ms. Gillibrand, the stakes this week are enormous. Their fund-raising pace is well behind what is necessary to reach 130,000 donors by September, which candidates must amass to qualify for the next round of debates.
Candidates must also receive at least 2 percent support in at least four qualifying polls to participate in the debates, scheduled for Sept. 12 and Sept. 13 in Houston. If 10 or fewer candidates qualify, the debate will take place on only one night.
Seven candidates have already locked down their spots: Mr. Biden, Ms. Warren, Mr. Sanders, Ms. Harris, Mr. Buttigieg, Mr. O’Rourke and, as of Monday, Mr. Booker.
Mr. Castro and Andrew Yang, an entrepreneur, have enough donors to qualify but need one more qualifying poll each. Ms. Klobuchar has crossed the polling threshold and is on pace to reach the donor threshold, according to her campaign, which said Monday that she had nearly 120,000 donors and was averaging 1,000 new donors a day.
But no other candidate has met either benchmark for the September debate, and none of them appear particularly close. Short of a breakout moment that translates into a surge of support over the next month, this week will be the last time they appear in a nationally televised debate for this race.