The 1878 law prohibits federal military personnel from working with state and local law enforcement. It has weathered sustained attacks following the September 11, 2001 attacks.

 

In 2007, Congress passed the John Warner National Defense Authorization Act. The legislation gave the president the authority to deploy federal troops to “restore public order and enforce the laws of the United States” during “a natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition.”

Following senator Patrick Leahy’s warning that changing the 1807 Insurrection Act “subverts solid, long-standing Posse Comitatus statutes that limit the military’s involvement in law enforcement, thereby making it easier for the president to declare martial law,” Congress repealed the changes and restored the Insurrection Act in its entirety, thus limiting presidential power during an emergency.

The latest effort to weaken Posse Comitatus unfolded earlier this month when Lt. Gen. Michael Barbero, head of the military’s Joint Improvised Explosive Device Defeat Organization, told a partially closed House Committee on Homeland Security hearing that terrorists with IEDs – Improvised Explosive Devices – now threaten the United States.