https://en.wikipedia.org/wiki/3rd_U.S.Infantry_Regiment(The_Old_Guard)

The 3rd United States Infantry Regiment is a regiment of the United States Army. It currently has three active battalions, and is readily identified by its nickname, The Old Guard, as well as Escort to the President. The regimental motto is Noli Me Tangere (from Latin: – "Touch Me Not"). The regiment is a major unit of the Military District of Washington (MDW).

https://en.wikipedia.org/wiki/United_States_Army_Military_District_of_Washington

The United States Army Military District of Washington (MDW) is one of nineteen major commands of the United States Army. Its headquarters are located at Fort Lesley J. McNair in Washington, D.C. The missions of the units in the Military District of Washington include ceremonial tasks as well as a combat role in the defense of the National Capital Region.

Besides Fort McNair, the following installations are included under the umbrella of the MDW's command:

Joint Base Myer–Henderson Hall, Virginia

Fort Belvoir, Virginia

Fort A.P. Hill, Virginia

Fort Meade, Maryland

Fort Hamilton, New York

The Military District of Washington also represents the U.S. Army in the Joint Force Headquarters National Capital Region (JFHQ-NCR), as well as oversight of all ceremonial operations in Arlington National Cemetery.

The current Commanding General of the Military District of Washington is Major General Omar J. Jones IV. The Military District of Washington Chief of Staff, and liaison to the JFHQ-NCR, is Colonel Brandon S. Robbins. The Commanding General, Chief of Staff, and Command Sergeant Major of the Military District of Washington hold the same positions at the JFHQ-NCR, which supervises military planning for the defense of the National Capital Region.

https://www.army.mil/article/171156/old_guard_battery_provides_presidential_ceremonial_salutes_with_a_bang