From Wikipedia: United States Marshals Service

I'm catching up on these guys. Among other things, they provide muscle for the judiciary. They date back to the Judiciary Act of 1789.

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The United States Marshals Service (USMS) is a federal law enforcement agency in the United States. The USMS is a bureau within the U.S. Department of Justice, operating under the direction of the Attorney General, but serves as the enforcement arm of the United States federal courts to ensure the effective operation of the judiciary and integrity of the Constitution. It is the oldest U.S. federal law enforcement agency created by the Judiciary Act of 1789 during the presidency of George Washington as the "Office of the United States Marshal". The USMS as it stands today was established in 1969 to provide guidance and assistance to U.S. Marshals throughout the federal judicial districts.

The Marshals Service is primarily responsible for the protection of judges and other judicial personnel, the administration of fugitive operations, the management of criminal assets, the operation of the United States Federal Witness Protection Program and the Justice Prisoner and Alien Transportation System, the execution of federal arrest warrants, and the protection of senior government officials through the Office of Protective Operations. Throughout its history the Marshals have also provided unique security and enforcement services including protecting African-American students enrolling in the South during the civil rights movement, escort security for United States Air Force LGM-30 Minuteman missile convoys, law enforcement for the United States Antarctic Program, and protection of the Strategic National Stockpile.