After the assassination of President John F. Kennedy, the Secret Service changed. Agent Clint Hill summed up the Secret Service's performance that afternoon:
There’s no question that we failed in providing protection for President Kennedy...
Several factors played into the tragic events of that afternoon. Agent Gerald Blaine noted that of a total of 330 agents, only "about 34 [were] on the White House detail." The agents were visibly present, running along side of the cars, but there was no way that they could talk or convey information between them other than using hand signals. They only had memorized pictures of those who might pose a threat to the President—plus their ability to work in teams...a far cry from what means the agency has at its disposal today.
Part of the difficulty was funding—Kennedy's assassination convinced Congress that the agency needed more money. Congress made changes as to who would be protected, and this included widows of presidents unless they remarried.
In 1965, Congress authorized the Secret Service...to protect former presidents and spouses during their lifetimes.
Children of former presidents were protected until they were sixteen years of age.
Agents on duty exhibited great bravery during John Kennedy's assassination. After Kennedy's death, the agency went on to train their agents differently.
Training, which until that time had been confined largely to "on-the-job" efforts, was systematized and regularized.
Other changes came about after the President was killed:
...no more travel in open automobiles and more agents, more money, and better communication.
The change of protecting presidential candidates did not exist until the assassination of Robert F. Kennedy. Though he had no agents protecting him, Robert Kennedy did have several bodyguards. At that point, nominees and candidates for president and vice-president were also to be protected.
With increased financing and ever-growing technology, Secret Service protection surrounding Presidents and their families, former Presidents and their spouses, and presidential candidates has changed—improving dramatically because of what occurred on November 22, 1963.