The 10th Democratic presidential debate took place Tuesday in Charleston, South Carolina, and two billionaires were at either end of the stage: Michael Bloomberg and Tom Steyer. Front-runner Bernie Sanders, who has made attacking the power of the “billionaire class” a central theme of his campaign, stood in the middle. It was a visual representation of the split within the Democratic Party, in which a growing number of people are “rising up against plutocracy,” says Anand Giridharadas, editor-at-large at Time magazine and author of “Winners Take All: The Elite Charade of Changing the World.”