Whenever he returned home from work, he would drive past the eternal flame at President Kennedy's grave at Arlington National Cemetery. "So it never left me. It's something you want to remember, because you don't want it to happen again. But you want to forget it because it happened. It's a paradox."

One he would not have been able to weather, he says, without the love and support of fellow agents.

"They would say to me, and it's hard for me to say without breaking down or tears coming to my eyes, 'Win, if it had to happen to anyone, we're glad it happened to you.' Because I was known for doing the best, most thorough advance in the entire agency. They know I would have done everything and more" to prevent what happened, he says.

"And I can't tell you how much that support has meant over the years." Lawson's desire to protect continues, even at 75. He handles security for a high-profile client whose name he declines to reveal. But nothing in the present can stop the litany of what-ifs involving the past.

When the president's day began at the Hotel Texas in Fort Worth, a persistent drizzle had forced the Secret Service to consider covering the motorcade's cars in Dallas with protective bubbletops. (Hours later, Dallas would end up sunny.)

Though the bubbletops were not bulletproof, the metal and the contour of the covering, says Lawson, would have made it difficult for a bullet to do much damage, and might have kept a gunman from even firing in the first place. So he's asked himself a million times:

Why couldn't it keep raining?

"I've spent years puzzling over thousands of what-if scenarios," he says. "Was there anything else I could have done? I guess I'll never have all the answers."

Idanell "Nellie" Brill grew up in Austin, where her father owned a leather-goods business. She enrolled at the University of Texas and met her college sweetheart, John Bowden Connally, whom she married on Dec. 21, 1940.

Connally became the first lady of Texas when her husband was elected governor in 1962. She holds the distinction of having said the last words President Kennedy ever heard.

As the president's car prepared to turn left onto Elm, she felt dazzled by the cheering throng and turned to share her enthusiasm, feeling like "a proud parent."

"Mr. President," she said, "you sure can't say Dallas doesn't love you."

He responded with a dazzling smile, followed only seconds later by gunfire.