The Secret Service's initial responsibility was to investigate counterfeiting of U.S. currency, which was rampant following the U.S. Civil War. The agency then evolved into the United States' first domestic intelligence and counterintelligence agency.
https://en.wikipedia.org/wiki/United_States_Secret_Service
Photo: Reuters/Jonathan Ernst. Pope Francis might be the most popular pontiff in a generation, but that doesn't mean he's easy to protect. It’s a lesson the U.S. Secret Service and other law enforcement organizations had to learn quickly as they prepared for Francis’ visit to the United States this week.
http://www.ibtimes.com/how-secret-service-protecting-pope-francis-snipers-undercover-agents-facial-2110767
The Secret Service is responsible for protecting all former presidents and their spouses. So, who else do they protect? By law, the Secret Service protects the president and his family, the vice president and her family, the president-elect and his family and the vice president-elect and her family. Former presidents and their spouses also get lifetime protection. A spouse will lose a Secret Service detail if he or she gets remarried.
http://minnesota.cbslocal.com/2015/04/23/good-question-just-who-gets-secret-service-protection/
The United States Secret Service (USSS) is an American federal law enforcement agency under the U.S. Department of Homeland Security. Until 2003, the Service was part of the U.S. Department of the Treasury.
https://en.wikipedia.org/wiki/United_States_Secret_Service
Joseph Clancy, director of the Secret Service, told reporters he traveled to Italy in June to get a feel for the best way to protect the leader of the Catholic Church, and the New York Police Department has been conducting highly publicized drills on how to respond to a terrorist attack or sudden power failure.
http://www.ibtimes.com/how-secret-service-protecting-pope-francis-snipers-undercover-agents-facial-2110767
Any of these individuals may decline Secret Service protection, except the President, the Vice President (or other officer next in the order of succession to the Office of President), the President-elect, and the Vice President–elect.
https://en.wikipedia.org/wiki/United_States_Secret_Service
Some members of the Swiss Guard will travel to the U.S. with Pope Francis, but his safety will be mostly in the hands of the Secret Service, which traditionally protects the president of the United States, political candidates and investigates financial crimes.
http://www.ibtimes.com/how-secret-service-protecting-pope-francis-snipers-undercover-agents-facial-2110767
The Secret Service will lead the security effort but it is also coordinating with the FBI and each city’s police department – help that will certainly be necessary as the Secret Service also stretches to protect the 200-or-so world leaders on hand for the United Nations General Assembly.
http://www.ibtimes.com/how-secret-service-protecting-pope-francis-snipers-undercover-agents-facial-2110767
After the 1901 assassination of President William McKinley, Congress also directed the Secret Service to protect the President of the United States. Protection remains the other key mission of the United States Secret Service.
https://en.wikipedia.org/wiki/United_States_Secret_Service
Former Presidents and their spouses for their lifetimes except when the spouse divorces or remarries. From 1997 until 2013, legislation became effective limiting Secret Service protection to former Presidents and their spouses to a period of 10 years from the date the former President leaves office.
https://en.wikipedia.org/wiki/United_States_Secret_Service
who do the secret service protect
The secret service protect is for the president and his family, the vice president and her family, the president-elect and his family and the vice president-elect and her family. Former presidents and their spouses also get lifetime protection. The president and his family, the vice president and her family, the president-elect and his family and the vice president-elect and her family, former presidents and their spouses are get the secret service protect.