July 16, 2016, 7:54 AM|In this Morning Rounds series, CBS News medical correspondent Dr. Jon LaPook and Dr. Tara Narula weigh in on a new warning by the American Heart Association that many commonly used medications could cause or worsen heart failure. Also, Dr. LaPook reports on a new study that examines how a physical cause may have driven former First Lady Mary Todd Lincoln’s mental struggles and erratic behaviors.