(CNN) – This month marks 50 years since the assassination of President John F. Kennedy, who was shot and killed by Lee Harvey Oswald in Dallas on Nov. 22, 1963.
Larry Sabato wrote a book about the assassination and says President Kennedy didn't have enough security that day.
"I make an argument in the book that his assassination was inevitable, because the thin blue line of protection was never thinner than around John F. Kennedy," Sabato said. "He wanted to mix and mingle with the people. That made him very vulnerable. There were only 12 secret service agents in a 12-mile motorcade in Dallas that day, passing 200,000 people that crowded into the roads and hundreds of open windows in buildings. This was almost inevitable."
Oswald was shot and killed three days after the assassination while in police custody.
There have been many conspiracy theories over the years about who might have been behind Kennedy's killing and if Oswald acted alone.