KINGSTREE, S.C. — One morning in late April, a small brick health clinic along the Thurgood Marshall Highway bustled with patients. There was Joshua McCray, 69, a public bus driver who, four years after catching covid-19, still is too weak to drive. Louvenia McKinney, 77, arrived complaining about shortness of breath. Ponzella McClary brought her 83-year-old mother-in-law, Lula, who has memory issues and had recently taken a fall. Morris Brown, the family practice physician who owns the clinic, rotated through Black patients nearly every 20 minutes. Some struggled to walk. Others pulled oxygen…