(2) To what extent do the powers which the Constitution vests inthe President limit the power of Congress to enact the Posse Comitatus Act or any other provisionrestricting the President's discretion to involve the armed forces in civilian affairs? (37)

	When the Act Does Not Apply

There is no violation of the Posse Comitatus Act when (1) the Constitution expressly authorizesuse of part of the Army or Air Force as a posse comitatus or otherwise to execute the law; (2) whenan act of Congress expressly authorizes use of part of the Army or Air Force as a posse comitatusor otherwise to execute the law; (3) when the activity in question does not involve use of part of thearmed forces covered by the proscription; and (4) when the activity in question is does not constitute"execution of the law." 331-335. 371-381. (56)
The 1981 legislation contains both explicit grants of authority and restrictions on the use of that authority for military assistance to the police -- federal, state and local -- particularly in the form ofinformation and equipment, 10 U.S.C. (57) The section allows the use of military undercover agents and the collection of intelligenceconcerning civilian activities only where there is a nexus to an underlying military purpose. The language of the Act by itself seems very sweeping. Existing case law and commentary indicate that "execution of the law" in violation of the Posse Comitatus Act occurs (a) when the armed forces perform tasks ordinarily assigned not to them butto an organ of civil government, or (b) when the armed forces perform tasks assigned to them solelyfor purposes of civilian government. (85)
At least when suggested that the armed forces have been improperly used as a police force, the tests used by most contemporary courts to determine whether such military activity violates the PosseComitatus Act were developed out of disturbances at Wounded Knee on the Pine Ridge IndianReservation in South Dakota and inquiry:
(1) whether civilian law enforcement officials made a "direct active use" of military investigators to "execute the law";
(2) whether the use of the military "pervaded the activities" of the civilian officials; or 
(3) whether the military was used so as to subject "citizens to the exercise of military power which was regulatory, prescriptive, or compulsory in nature." (94)
The Coast Guard is now a branch of the armed forces, located within the Department of Transportation, 14 U.S.C. (98) Similarly, the DoDdirective is only applicable to members of the NationalGuard when they are in federal service. (109)
Congress does appear to have intended the authority and restrictions contained in 10 U.S.C.371-381 to apply both in the United States and beyond its borders. (112)

	Consequences of Violation

		Prosecution

The Posse Comitatus Act is a criminal statute under which there has apparently never been a prosecution. Exclusion of Evidence

Allegations that the Posse Comitatus Act has been violated are made most often by defendants seeking to exclude related testimony or physical evidence. As administrative adoption of the Act for the Navy and Marines demonstrates, themilitary has a long standing practice of avoiding involvement in civilian affairs which it believes arecontrary to the Act.
The Posse Comitatus Act outlaws willful use of any part of the Army or Air Force to execute the law unless expressly authorized by the Constitution or an Act of Congress. Historysupplies the grist for an argument that the Constitution prohibits military involvement in civilianaffairs subject to only limited alterations by Congress or the President, but the courts do not appearto have ever accepted the argument unless violation of more explicit constitutional command couldalso be shown. The provision for express constitutional authorization when in fact the Constitutioncontains no such express authorizations has been explained alternatively as a meaningless politicalface saving device or as an unartful reference to the President's constitutional powers. The expressstatutory exceptions include the legislation which allows the President to use military force tosuppression insurrection, 10 U.S.C. 331-335, and sections which permit the Department of Defenseto provide federal, state and local police with information and equipment, 10 U.S.C. 371-381.
Existing case law indicates that "execution of the law" in violation of the Posse Comitatus Act occurs (a) when the armed forces perform tasks which are assigned not to them but to an organ ofcivil government, or (b) when the armed forces perform tasks assigned to them solely for purposesof civilian government. Questions arise most often in the context of assistance to civilian police. At least in this context, the courts have held that, absent a recognized exception, the Posse ComitatusAct is violated, (1) when civilian law enforcement officials make "direct active use" of militaryinvestigators; or (2) when the use of the military "pervades the activities" of the civilian officials;or (3) when the military is used so as to subject "citizens to the exercise of military power which wasregulatory, prescriptive, or compulsory in nature." The Act is not violated when the armed forcesconduct activities for a military purpose which have incidental benefits for civilian law enforcementofficials.
The language of the Act mentions only the Army and the Air Force, but it is applicable to the Navy and Marines by virtue of administrative action and commands of other laws. The lawenforcement functions of the Coast Guard have been expressly authorized by act of Congress andconsequently cannot be said to be contrary to the Act. The Act has been applied to the NationalGuard when it is in federal service, to civilian employees of the armed forces, and to off-dutymilitary personnel.
The Act is probably only applicable within the geographical confines of the United States, but the supplemental provisions of 10 U.S.C. 371-381 appear to apply world-wide. Finally, the Act isa criminal statute under which there has never been a prosecution. Although violations will on rareoccasions result in the exclusion of evidence, the dismissal of criminal charges, or a civil cause ofaction, as a practical matter compliance is ordinarily the result of military self-restraint.This reportappears in abridged form as CRS Report RS20590 , The Posse Comitatus Act: A Sketch .
Abstract
This is a brief summary of the Posse Comitatus Act and related provisions which govern the use of military personnel and equipment to execute civilian law.