Four Democrats vying for their party’s presidential nomination honed in on the economic concerns of the black community during a forum Saturday in South Carolina, a state where nonwhite voters will play a major role in next year’s primary election. Appearing on stage one at a time, Sens. Cory Booker of New Jersey and Elizabeth Warren of Massachusetts, Mayor Pete Buttigieg of South Bend, Indiana, and former Texas Rep. Beto O’Rourke all stressed the need to increase access to capital for black business owners as part of a broader effort to address wealth inequality. Warren expounded on what she’s called...