DALLAS — For retired Secret Service agent Winston G. Lawson, the memory of Nov. 22, 1963, is an endless stream of windows. "From Love Field to Dealey Plaza," he says, "there were 20,000 windows. How could we possibly check them all?"

For TV cameraman Mal Couch, then a precocious 25, seeing the rifle that he believes killed President John F. Kennedy — its barrel sticking out of one of those windows — marked "the beginning of the end of the world."

Lawson, 75, and Couch, 65, are survivors of a presidential motorcade that began in splendor and ended in horror.

Forty years have passed — a span of two generations, a lifetime for some — since JFK's assassination. But for the people caught in the maelstrom of the motorcade, the horrific day comes to life not only in the passages of a textbook or the images of a documentary.

It lives within them because it transformed them.

For Nellie Connally, 84, the only surviving passenger of the Lincoln convertible that carried the president and his dazzling first lady, Jacqueline Bouvier Kennedy, the 40 years since have made her circumspect and fearful, something she never was before.

"Since that day, I have never fully stopped looking over my shoulder at the horror that might be behind me," says the widow of former Texas Gov. John Connally, who was critically wounded in the shooting that killed the president.

Bobby Hargis, 72, then a Dallas police officer whose motorcycle flanked the left rear bumper of the president's car, has a recurring dream in which he chases but never quite catches Lee Harvey Oswald.

For Hargis, the ensuing years have taken him on his own spiritual journey. "It makes you think about life," he says, sitting at his breakfast table in Cleburne, Texas. "The shortness of it, the preciousness of it, every breath we take. And what did I learn that day? That we're never that far away from being nothing."

For Jim Wright, 80, former speaker of the U.S. House of Representatives, the events of that day cut short the life of a president he loved — a friend — and in their own crude way, reshaped the course of history.

"I was in such an ebullient mood that day. Cloud nine!" said Wright, who teaches at Texas Christian University. "Wow! And then, in such a short time, I would be plunged to the pit of despondency, numbing sadness, pathos. In many respects, none of us has ever been the same since that moment.

"And it won't leave our minds, no matter how hard we try."