It was Nov. 25, 1963. Army Sgt. Keith Clark, the Army bugler assigned to sound taps at John F. Kennedy's funeral, had the most important and solitary task of his life: Sound the 24 notes of the venerable melody that would close the nation's wrenching, four-day farewell to its assassinated president. But the pressure, the cold and the wait told on Sgt. Clark that day 50 years ago this month.