Democratic presidential hopeful Pete Buttigieg, mayor of South Bend, Ind., (left) and entrepreneur Andrew Yang (center) listen as former Texas Rep. Beto O’Rourke speaks during the fourth Democratic primary debate.

Democratic presidential hopeful Pete Buttigieg, mayor of South Bend, Ind., (left) and entrepreneur Andrew Yang (center) listen as former Texas Rep. Beto O’Rourke speaks during the fourth Democratic primary debate.