Four Black candidates have qualified for the closely watched Democratic Primary in Florida’s 20th Congressional District. As a result, U.S. Rep. Debbie Wasserman Schultz, who is the longest-serving Democrat in Florida’s congressional delegation, is now the only White candidate in a crowded race. Other candidates include Luther Campbell, a rapper who became a community leader, former U.S. Rep. Sheila Cherfilus-McCormick, former Broward County May…