Nov. 22 will mark the 50th anniversary of the assassination of President John F. Kennedy in Dallas, a moment that left an indelible mark on those who remember it.
It also permanently changed the agency charged with protecting the president — the U.S. Secret Service.
Looking back at the images of Kennedy, first lady Jackie Kennedy, Texas Gov. John Connally and his wife waving as they rode through the streets of Dallas in an open Lincoln, it all looks terribly innocent and naive.
Less than a year after Lee Harvey Oswald fired from the sixth floor of the Texas School Book Depository, the Warren Commission formed by President Lyndon Johnson completed its investigation into that day.
The commission found what it politely called "certain shortcomings and lapses from the high standards which the Commission believes should prevail in the field of Presidential protection."
Many dealt with the Secret Service's advance work. No one thought to check the buildings along the motorcade route. There were no formal procedures for working with local law enforcement agencies.
Marc Ambinder, who is editor at large of The Week and has written about the agency, says the Secret Service of 50 years ago was ill-prepared to deal with the gregarious Kennedy.
"It's a combination of the fact that the Secret Service playbook was outdated and they had never really encountered a president before John F. Kennedy who loved to mix it up, and loved to get in the middle of huge crowds, and fed off the energy of huge crowds," Ambinder says.
After the assassination, the Secret Service made some immediate changes. Open limousines were out. And it began taking a more aggressive approach to its advance work.
"Not criticizing what happened in 1963, but I think it's fair to say that protections changed quite a bit, and how we do things on a day-to-day basis," says Special Agent Brian Leary, who serves as a spokesman for the agency.
The Secret Service began staffing up. There were just 28 agents on the ground in Dallas in 1963, and the agency's budget was $5.5 million. Last year the budget was more than $1.6 billion.
Over the years, Leary says, the service has established counter-sniper units, assault teams and surveillance units.
"So as the threat has evolved and has changed, Secret Service has changed with it," he says.
In fact, it's hard to compare the bubble that surrounds President Obama with the Kennedy-era security. Now anyone hoping to get close to the president has to go through a metal detector and a bag check. The president rides in a limousine so armored it's referred to as "the Beast."
Ambinder, who has been allowed behind the scenes of a number of Secret Service operations, says the advance work for just one short motorcade is meticulous.
"The Secret Service advance machine puts together an enormous, thick presidential transportation manual — just for that one movement — that's maybe 60 to 70 pages long that has information about relocation sites and contingencies, and what happens if the motorcade needs to be diverted, and what happens if there's a chemical attack," he says. "Just in that one movement."
Leary says the Secret Service tries each day to apply the lessons from Dallas and subsequent attempts on the president's life.
"I think there's certainly a recognition that that was a tragic day for the nation and a very difficult day for the Secret Service," he says. "But with all of that, whether that was the assassination of President Kennedy or the attempted assassination of President Reagan, Secret Service is trying to learn from those events."
And as if protecting the president's life wasn't enough, over the years the Secret Service has been given the added duty of guarding presidential families, visiting heads of state and presidential candidates.
And that's all in addition to its original task: investigating counterfeiters.