(By Larry J. Sabato, politics professor and director of U.Va.’s Center for Politics) Fifty years ago this month, something happened that became a “flashbulb moment” for every American alive at the time and old enough to remember anything. The indelible images — in books, movies and television — and the detailed personal accounts by millions who recall precisely where they were and what they were doing when they heard about President John F. Kennedy’s assassination have been passed on to succeeding generations.