Here Are the Lineups for the Next Democratic Debates

There will be a round two for Joseph R. Biden Jr. versus Senator Kamala Harris.

After Ms. Harris’s criticism of Mr. Biden’s record on race issues dominated the story line following the first Democratic presidential debate last month, the two will square off again later this month in Detroit when candidates gather for the second set of debates.

In a television spectacle that CNN is unlikely to nominate for upcoming awards shows, the cable network spent 40 minutes dividing the 20 qualifying candidates into two groups.

The debate’s first group, which will appear July 30, includes eight candidates running as moderate pragmatists, along with the field’s two highest-profile liberals, Senator Elizabeth Warren of Massachusetts and Senator Bernie Sanders of Vermont.

The second group, which will go July 31, has Mr. Biden and Ms. Harris, as well as Senator Cory Booker of New Jersey and Julián Castro, the former housing secretary, whose campaign surged following his performance in the June debate.

The top 5 matchups to watch

Biden vs. Harris: Mr. Biden, the former vice president, was caught unprepared for the frontal attack by Ms. Harris, of California, on his record on race issues last month.

Sanders vs. Warren: The top liberals in the race, the two senators met privately before their campaigns began and agreed not to attack each other. That peace treaty will be put to the test as they stand next to each other at the center of the first night’s debate stage.

Klobuchar vs. Buttigieg: Senator Amy Klobuchar of Minnesota has made little secret of her displeasure that lesser-experienced male candidates like Mayor Pete Buttigieg of South Bend, Ind., and Beto O’Rourke, the former Texas congressman, received gobs of media attention that has yet to come her way. Now she will be standing next to Mr. Buttigieg, and have her chance to take him down a peg.

Booker vs. Biden: Before Ms. Harris went after Mr. Biden during the first debate, it was Mr. Booker who demanded he apologize for praising segregationist senators. But unlike Ms. Harris, Mr. Booker didn’t sustain the attack. Now he will have a chance, as he stands next to the former vice president.

Inslee vs. the moderators: Gov. Jay Inslee of Washington has made his campaign a crusade to discuss climate change, a topic that received little airtime in the first set of debates. Expect a lot of griping from him about the topic getting short shift, no matter how much it is discussed in Detroit.

How did they draw the names?

CNN divided the field into two groups of 10 candidates as only the network could. There were dark blue cards and light blue cards, and three tiers of candidates, each with their own box to be drawn from. (The campaigns were allowed to inspect the boxes before the drawing, a person involved in the inspection said.)

In what could have passed for a parody of an N.F.L. pregame show, the network showed three simultaneous camera shots of the live drawing, so viewers at home could see the inside of the box as well as the CNN personality as they lifted the cards out.

And there was plenty of commentary about who might wind up on which night before the cards were drawn — a delay to add tension to what was, literally, picking names out of a box.

The spectacle may wind up being a one-time-only event. Just six candidates have qualified for the party’s September debate in Houston. If 10 or fewer reach the polling and fund-raising threshold, that debate (and likely subsequent ones) will air on just a single night.

And the drawing, hokey as it may have seemed as live television programming, was a high-stakes event. Next week is likely to be the last time many of the candidates will appear on a presidential debate stage in this election cycle. And the first set of debates proved that drawing a successful contrast with an opponent can provide rocket fuel for a campaign.

Tom Perez, the chairman of the Democratic National Committee, has raised the threshold to participate in the party’s third debate, in September. Candidates must receive contributions from 130,000 donors and earn at least 2 percent support in at least four qualifying polls to participate.

How will the second debates differ from the first?

CNN announced last week that it will forbid the sort of raise-your-hand questions that led to a stage of Democratic presidential candidates announcing their support for extending federal health insurance benefits to undocumented immigrants.

CNN will also not ask down-the-line questions like NBC, which asked each candidate to provide one-word responses to the same query.

(Mr. Biden on Monday pooh-poohed the NBC format. “I’m not doing any more raise-your-hand questions,” he told an audience in Des Moines.)

The network also said it will penalize any candidate who “consistently interrupts” by reducing the amount of time he or she is allowed to speak.

Given the obvious benefit of interrupting to draw contrasts with debate opponents, it remains to be seen how effective this rule will be.

What lessons did candidates learn the last time around?

An onstage attack, skillfully delivered, can turn a struggling candidate into one on the rise.

Ms. Harris raised nearly one-third of her campaign’s second-quarter fund-raising total in the week after she attacked Mr. Biden during the June debate.

Mr. Castro said Sunday that his campaign had accrued 60,000 donors since he went after Mr. O’Rourke’s immigration position — enough to push Mr. Castro past the 130,000-donor threshold to qualify for the September debate. (He has yet to meet the polling requirement.)

Mr. Castro, during an interview on Sunday in Cedar Rapids, Iowa, said his first debate performance put him “on a lot more radar screens and a lot more lists of people’s three or four top candidates.”

Other candidates, he said, will likely be prepared to emulate his success when they gather in Detroit.

“As you move up,” he said, “you’re probably more subject to potential attacks.”

Matt Stevens contributed reporting.