From Geoffrey Klingsporn’s “The Secret Posse” (Legal Affairs: March/April 2005):
What do these scenarios have in common? Under current military policy, both fall under the heading of “Information Operations,” officially defined as “actions taken to affect adversary information and information systems while defending one’s own information and information systems.” …
The law that, in effect, prevents the Army from acting as a national police force is the Posse Comitatus Act, an 1878 statute that prohibits law enforcement officers from using military personnel as a posse comitatusâ€â€Latin for “power of the county” or, in the vernacular of the Old West, a “posse”â€â€to enforce domestic law, except with the express authorization of the president or Congress. …
“The use of military forces to seize civilians,” wrote the U.S. Court of Appeals for the Eighth Circuit, “can expose civilian government to the threat of military rule and the suspension of constitutional liberties,” and can chill free speech and other fundamental rights, creating the atmosphere of an enemy occupation. …
Since the 1980s, though, the statute has been weakened by laws that allow the military to help address the problems of drug trafficking, natural disasters, and terrorist attacks. It is now routine for soldiers and sailors to help state and local police with training, equipment, and logistics; to detect and monitor suspected smugglers; and to keep order in disaster areas. … But the courts generally have ruled that it is well within the discretion of the president and Congress to allow the military to help in nonmilitary situations, including cases of terrorism. In 1988, a federal district judge in Washington, D.C., ruled that the Posse Comitatus Act was not violated when the FBI used the Navy to help capture a suspected terrorist in international waters and transport him to the United States.