The original 1878 Posse Comitatus Act was indeed passed with the intent of removing the Army from domestic law enforcement. "Posse Comitatus" means the "power of the county," reflecting the inherent power of the old west county sheriff to call upon a posse of able-bodied men to supplement law enforcement assets and thereby maintain the peace. Following the Civil War the Army had been used extensively throughout the South to maintain civil order, to enforce the policies of the reconstruction era, and to ensure that any lingering sentiments of rebellion were crushed. However, in reaching those goals the Army necessarily became involved in traditional police roles and in enforcing politically volatile reconstruction era policies. The stationing of federal troops at political events and polling places under the justification of maintaining domestic order became of increasing concern to Congress, which felt that the Army was becoming politicized and straying from its original national defense mission. The Posse Comitatus Act was passed to remove the Army from civilian law enforcement and to return it to its role of defending the borders of the United States.
APPLICATION OF THE ACT
In order to understand the extent to which the Act has relevance today, it is important to understand to whom the Act applies and under what circumstances. The statutory language of the Act does not apply to all U.S. military forces. While the Act has applicability to the Army, Air Force, Navy, and Marines, including their reserve components, it does not have any applicability to the Coast Guard, nor to the huge military manpower resources of the National Guard. The National Guard, when it is operating in its state status pursuant to Title 32 of the U.S. Code is not subject to the prohibitions on civilian law enforcement. (Federal military forces operate pursuant to Title 10 of the U.S. Code.) In fact one of the express missions of the Guard is to preserve the laws of the state during times of emergency when regular law enforcement assets prove inadequate. It is only when federalized pursuant to an exercise of Presidential authority that the Guard becomes subject to the limitations of the Posse Comitatus Act.
The intent of the Act is to prevent the military forces of the U.S. from becoming a national police force or guardia civil. Accordingly, the act prohibits the use of the military to "execute the laws"., Execution of the laws is perceived to be a civilian police function, which includes the arrest and detention of criminal suspects, search and seizure activities, restriction of civilian movement through the use of blockades or checkpoints, gathering evidence for use in court, and the use of undercover personnel in civilian drug enforcement activities.
The federal courts have had several opportunities to define what behavior by military personnel in support of civilian law enforcement is permissible under the Act. The test applied by the courts has been to determine whether the role of military personnel in the law enforcement operation was "passive" or "active". Active participation in civilian law enforcement, such as making arrests, is deemed to be a violation of the Act, while taking a "passive" supporting role is not. Passive support has often taken the form of logistical support to civilian police agencies. Recognizing that the military possesses unique equipment and uniquely trained personnel, the courts have held that providing supplies, equipment, training, facilities, and certain types of intelligence information does not violate the Act. Military personnel may also be involved in the planning of law enforcement operations, as long as the actual arrest of suspects and seizure of evidence is carried out by civilian law enforcement personnel.
The Posse Comitatus act was passed in the Nineteenth Century, when the distinction between criminal law enforcement and defense of the national borders was clearer. Today, with the advent of technology that permits weapons of mass destruction to be transported by a single person, the line between police functions and national security concerns has blurred. As a matter of policy Western nations have labeled terrorists as "criminals" to be prosecuted under domestic criminal laws. Consistent with this, the Department of Justice has been charged as the lead U.S. agency for combating terrorism. However, all terrorist acts are not planned and executed by non-state actors. Terrorism refers to illegal attacks on civilians and other non-military targets by either state or non-state actors. This new type of threat requires a reassessment of traditional military roles and missions along with an examination of the relevance and benefit of the Posse Comitatus Act.
EROSION OF THE ACT
While the Act appears to prohibit active participation in law enforcement by the military, the reality in application has become quite different. The Act is