CNN, which is broadcasting the debates, assigned candidates randomly with a drawing Thursday night, with 10 candidates spread evenly over two events scheduled July 30-31 and held in Detroit.

Former Vice President Joe Biden and Senator Kamala Harris of California will take center stage July 31, barely a month after Harris jolted the sprawling field in the first debates and propelled herself to clear top tier status with an aggressive takedown of the 76-year-old Biden’s long record on race.

ATLANTA — The second set of summer Democratic presidential debates will feature a rematch with a twist, plus the first showdown of leading progressives as the party wrestles with its philosophical identity and looks ahead to a 2020 fight against President Trump.


This time, Harris, the lone black woman in the field, will be joined by another top black candidate, Senator Cory Booker of New Jersey, who also has been an outspoken critic of Biden. Booker had denounced Biden for his recollections of the ‘‘civility’’ of working in a Senate that included white supremacists and for his leadership on a 1994 crime bill that Booker contends assailed as a mass incarceration agent in the black community.

Meanwhile, Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont will headline the July 30 lineup, allowing the two progressive icons to compete directly for the affections of the party’s left flank. They will be joined by several more moderate candidates who are likely to question the senators’ sweeping proposals for single-payer health insurance and tuition-free college, among other plans.

Flanking Sanders and Warren on the first night will be former representative Beto O'Rourke of Texas, Governor Steve Bullock of Montana, Pete Buttigieg, former representative John Delaney, former Colorado governor John Hickenlooper, Senator Amy Klobuchar of Minnesota, Representative Tim Ryan of Ohio, and author Marianne Williamson.


It will be the first debate opportunity for Bullock, who takes the spot that Representative Eric Swalwell of California had in June before dropping out of the race. Another late entry to the campaign, billionaire activist Tom Steyer, did not meet the polling or fundraising thresholds required for the July debate.

On the second night, Biden and Harris will be joined by Booker, New York City Mayor Bill de Blasio, Senator Michael Bennet of Colorado, former Obama Cabinet member Julián Castro, Senator Kirsten Gillibrand of New York, Representative Tulsi Gabbard of Hawaii, Governor Jay Inslee of Wisconsin, and entrepreneur Andrew Yang.