2020 debates: Biden-Harris rematch and progressive faceoff

Democratic presidential candidate Sen. Kamala Harris, D-Calif., greets an audience member after speaking at a Women of Color roundtable, Tuesday, July 16, 2019, in Davenport, Iowa. (AP Photo/Charlie Neibergall)

An audience member takes a photo of Democratic presidential candidate former Vice President Joe Biden during a community event, Wednesday, July 17, 2019, in Council Bluffs, Iowa. (AP Photo/Charlie Neibergall)

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.