Congress passed the Posse Comitatus Act more than 130 years ago to restrict the use of military personnel on U.S. soil, and the nation has long possessed an aversion to armed forces being relied upon for enforcement actions against civilians. But the spirit of the law since that time has been subject to different interpretations and is explored in depth in a recent report [PDF] by the Congressional Research Service.
“The USA PATRIOT Act broadened the permissible circumstances for the use of the military to assist law enforcement agencies in countering terrorism,” the report states, “but Congress also reaffirmed its determination to maintain the principle of the posse comitatus law. The perceived breakdown in civil law and order in Hurricane Katrina’s wake evoked more calls to reevaluate the military’s role in responding to disasters.”
Despite those calls, the report says the Posse Comitatus Act has remained largely unchanged since it passage, though plenty of exceptions exist, too – such as one that allows the armed forces to be used in response to an insurrection. The California National Guard turned out in 1992 after the acquittal of Los Angeles police officers who beat motorist Rodney King led to angry riots in the streets.