This month marks the 40th anniversary of President John F. Kennedy's assassination in 1963. Surveys consistently show that event profoundly affected the outlook of an entire generation of Americans, much as 9/11 has the current one.

As the Kennedy murder slowly recedes further into the past, we would be wise to review its lessons. That dark event, the bizarre circumstances that surrounded it, and the indelible dark stain it put on America's soul should prove instructive to us today as we battle the shadowy network of terrorists that haunts us.

An older generation of Americans may recall that in the weeks leading up to the assassination, many political and other public figures expressed concerns about Kennedy's trip to Dallas in November 1963. There was a palpable but undefined mood of uneasiness hanging in the air then; a feeling that something was wrong, although no one could quite define it. Adlai Stevenson, then the U.S. ambassador to the United Nations, had been shouted at and spat upon by an angry crowd in Dallas not long before Kennedy's appearance. It was like a Shakespearean omen of approaching doom.

Another dramatic irony was even spookier: The one person who seemed to read the signs, though perhaps unwittingly, may have been Kennedy himself. First, as he arrived at his hotel in Fort Worth, Texas, the day before he was shot, a surging crowd of well-wishers swarmed the president and first lady as they made their way into the building (presidential security was amateurish compared to today).

As documented in William Manchester's masterful book "The Death of a President," Kennedy came close to prophesizing his own death the next morning as he recalled the crowd outside the hotel the previous day. He observed to his wife and several gathered aides that the disorderly crowd had presented an ideal opportunity for an assassin to strike. He even mimicked someone pulling a trigger and then dropping the gun.

A coincidence, some say. Others say no, the threat of an attempt on his life was weighing on Kennedy's mind. But surely no one in the president's entourage really believed an historic tragedy was about to take place. The rest is history.

The Kennedy assassination terrorized Americans similar to the way 9/11 has scared us today. In both cases, unimaginable violence struck U.S. shores in ways that still aren't completely explained, especially in the case of Kennedy. Both events deeply disillusioned and frightened our nation. Was Kennedy's killing the work of one deranged man, or an unexplained conspiracy against the United States as a whole? Was 9/11 the beginning of another, even greater conspiracy?

Also in the cases of both 1963 and 2001, endless questions have been posed about whether intelligence was ignored that should have told authorities what was coming. Yet in both cases, no such evidence has been revealed. Continued...