Authorization
Today, the Secret Service is authorized by law to protect: the President, the Vice President, (or other individuals next in order of succession to the Office of the President), the President-elect and Vice President-elect; the immediate families of the above individuals; former Presidents, their spouses for their lifetimes, except when the spouse re-marries.[My words ... this means Hillary unless she remarries]
In 1997, Congressional legislation became effective limiting Secret Service protection to former Presidents for a period of not more than 10 years from the date the former President leaves office. [My words .... A new law like this would start with the next President.]
Children of former presidents until age 16; visiting heads of foreign states or governments and their spouses traveling with them, other distinguished foreign visitors to the United States, and official representatives of the United States performing special missions abroad;
Major Presidential and Vice Presidential candidates, and their spouses within 120 days of a general Presidential election.
And the next president to retire AFTER 1997 was Bill Clinton.
And the reason I know this is because I called Senator Thurmond's office and asked.