Secret Service, United States
United States Secret Service, a law enforcement division (since 2003) of the Dept. of Homeland Security. It was established in 1865 in the the Dept. of the Treasury to investigate and prevent counterfeiting of currency, officially becoming a distinct organization within the department in 1883. The Secret Service enforces federal laws relating to currency, coins, obligations, and the securities of the United States and foreign governments, including forgery and fraudulent electronic transfer. After the assassination of President William McKinley in 1901, the force was charged with protecting the president. This protection was later extended to the members of the immediate families of the president, vice president, president-elect, and vice president–elect; major presidential and vice presidential candidates; former presidents and their spouses; widows of former presidents until their death or remarriage; minor children of a former president; and visiting heads of state.
See study by J. Bamford (1983).