The original intent of the US Secret Service had little to do with protection. At first, the agency’s sole intent was to investigate and prevent counterfeiting of US dollars. In 1901, however, President William McKinley was assassinated, and one result of this was assigning Secret Service agents to protect the life and well-being of the subsequent presidents. Since then, protection has been extended to other government officials, some well-known politicians and visiting dignitaries, and former presidents and their families, at least for some period of time.
There are a few people who always receive protection, including the current US president, vice president, and sometimes other high-ranking officials who might succeed the president. For instance, the speaker of the house might, under some circumstances, be entitled to Secret Service protection, especially if a situation arose where the vice president or president were in danger. Wives of the president and vice president, and their children under age 16, are entitled to protection too.
At one time, former presidents received Secret Service protection for life. This changed in 1996, and now former presidents and first ladies are only entitled to this protection for ten years after their service to the country. The protection can continue, however, especially if ordered by the current president. Essentially, the president has the authority to extend protection to anyone or to any event, such as a meeting of high-ranking officials, that might carry potential danger. Also, presidents in office may extend it to all of their children, not just those under the age of 16.
Vice presidents typically do not have Secret Service protection after their term of service is up, unless some threat or danger exists. If the vice president runs for the office of president, however, he or she — and all other major candidates in the primary and general presidential election — are likely to receive protection. Just how soon this is provided may be based in part on the profile of the candidate and any possible early threats, which are not that uncommon, to a candidate’s life.
Another way in which the Secret Service functions is to protect foreign heads of state or visiting dignitaries with high profiles. Visits may be arranged contingent on guarantees of protection, though heads of state may also bring their own version of the Secret Service with them. When a number of foreign dignitaries meet with the president, additional Secret Service agents are usually employed to create the safest environment possible for all concerned.
Some people are allowed to refuse protection if they do not desire it. Though President Clinton has lifetime protection, and is the last president to receive it, unless laws change, he could refuse the services of Secret Service members. Generally, a president or vice president in office cannot refuse protection because of the high security nature of these positions.