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 Donald Trump.

Former Vice President Joe Biden and California Sen. Kamala Harris 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.

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.

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This time, Harris, the lone black woman in the field, will be joined by another top black candidate, New Jersey Sen. Cory Booker, 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 the New Jersey senator contends assailed as a mass incarceration agent in the black community.

Meanwhile, Sens. Bernie Sanders and Elizabeth Warren 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 Texas Rep. Beto O'Rourke; Montana Gov. Steve Bullock; Mayor Pete Buttigieg of South Bend, Indiana; former Rep. John Delaney; former Colorado Gov. John Hickenlooper; Minnesota Sen. Amy Klobuchar; Ohio Rep. Tim Ryan; and author Marianne Williamson.

It will be the first debate opportunity for Bullock, who takes the spot that California Rep. Eric Swalwell had in June before dropping out in recent weeks. Another late entry to the race, 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; Colorado Gov. Michael Bennet; former Obama Cabinet member Julián Castro; New York Sen. Kirsten Gillibrand; Hawaii Rep. Tulsi Gabbard; Washington Gov. Jay Inslee; and entrepreneur Andrew Yang.

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