The United States Secret Service (USSS) is a federal law enforcement agency under the Department of Homeland Security with two core missions: protecting national leaders and investigating financial crimes. Originally part of the Department of the Treasury (until 2003) due to its initial mandate to combat rampant counterfeit currency after the Civil War, the agency has safeguarded American presidents and presidential candidates since 1901. Its protective mission covers presidents, vice presidents, their families, former presidents, visiting heads of state, and even the White House complex, with the president and vice president legally unable to refuse this security. On the investigative side, it tackles counterfeiting, cybercrime, identity theft, and financial fraud, while also partnering with the FBI's Joint Terrorism Task Force and investigating missing children cases. As of July 2024, the agency protects 36 individuals, and it leads security operations for National Special Security Events—making it one of the few agencies that both guards the nation's top leaders and secures its financial infrastructure.