WASHINGTON — By now, most of the world has digested the 50th anniversary of John F. Kennedy’s assassination, and millennials can sigh relief that another such re-examination is at least 10 years away. While most recent books and films have covered Kennedy’s life and the mysteries that remain, an equally compelling exploration is why people who were alive and cognizant at the time are still obsessed with events surrounding the 35th president. What is it that makes his presidency and death so profound for millions?