Military Powers Explorer

The Constitution gives Congress the power “To declare War.” Constitution Annotated

The Constitution makes the president “Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States.” Constitution Annotated

The Posse Comitatus Act makes it a crime to willfully use any part of the Army, Navy, Marine Corps, Air Force or Space Force “as a posse comitatus or otherwise to execute the laws,” except “in cases and under circumstances expressly authorized by the Constitution or Act of Congress.” U.S. Code

This is a general explanation of the law. It isn’t an assessment of any real deployment, event or official, and it isn’t legal advice.

The Posse Comitatus Act

• The Posse Comitatus Act makes it a crime to willfully use any part of the Army, Navy, Marine Corps, Air Force or Space Force “as a posse comitatus or otherwise to execute the laws,” except “in cases and under circumstances expressly authorized by the Constitution or Act of Congress.” U.S. Code
• A violation is punishable by a fine, up to two years in prison, or both. U.S. Code
• The act traces to a law passed in 1878. U.S. Code
• Until a 2021 amendment, the act named only the Army and the Air Force. The amendment added the Navy, the Marine Corps and the Space Force. U.S. Code
• When the military supports civilian law enforcement under Chapter 15 of Title 10, the defense secretary must issue rules so the support doesn’t include or permit direct participation by a member of the Army, Navy, Air Force or Marine Corps in a search, seizure, arrest or similar activity, unless that participation is otherwise authorized by law. U.S. Code

The Insurrection Act

• The Constitution Annotated traces 10 U.S.C. 251 to 254 to laws Congress passed in 1795 and 1807 authorizing the president to employ military force in the execution of the laws. Constitution Annotated
• The Constitution gives Congress the power “To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions.” Constitution Annotated
• The 1795 law that delegated to the president the power to call out the militia was held constitutional. Constitution Annotated
• When there is an insurrection in a state against its government, the president may, at the request of the state’s legislature, or of its governor if the legislature can’t be convened, call into federal service the militia of other states, in the number the state requests, and use the armed forces the president considers necessary to suppress the insurrection. U.S. Code
• When the president considers that “unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States” make it impracticable to enforce federal law in any state by the ordinary course of judicial proceedings, the president may call into federal service any state’s militia and use the armed forces the president considers necessary to enforce those laws or suppress the rebellion. U.S. Code

The president, using the militia, the armed forces, both or any other means, must take the measures the president considers necessary to suppress, in a state, “any insurrection, domestic violence, unlawful combination, or conspiracy” that does either of the following: U.S. Code

• It so hinders the execution of state and federal law in the state that any part or class of its people is deprived of a right, privilege, immunity or protection named in the Constitution and secured by law, and the state’s authorities are unable, fail or refuse to protect it. In that case, the state is considered to have denied the equal protection of the laws. U.S. Code
• It opposes or obstructs the execution of federal law or impedes the course of justice under those laws. U.S. Code
• Whenever the president considers it necessary to use the militia or the armed forces under Chapter 13 of Title 10, “Insurrection” (10 U.S.C. 251 to 255), the president must, by proclamation, immediately order the insurgents “to disperse and retire peaceably to their abodes within a limited time.” U.S. Code
• For these sections, “State” includes Guam and the Virgin Islands. U.S. Code
• In 2008, Congress rewrote 10 U.S.C. 253 (then 333), part of the Insurrection Act, removing provisions that had authorized the president to employ the armed forces during a natural disaster or terrorist attack. U.S. Code
• In Martin v. Mott (1827), the Supreme Court asserted that the president’s judgment was final on whether the facts called for using the powers a 1795 militia law gave the president. Constitution Annotated

National Guard Status: State, Title 32 and Federal

• The Army National Guard and Air National Guard are part of the organized militia of the states, territories, Puerto Rico and the District of Columbia. They are organized, armed and equipped wholly or partly at federal expense. U.S. Code
• States have a concurrent power to aid the national government by calling out the militia under their own authority, and in emergencies they may use the militia to put down armed insurrection. Constitution Annotated
• Full-time National Guard duty, one Title 32 status, is training or other duty, other than inactive duty, performed as a member of a state’s or territory’s National Guard, under sections of Title 32 that include Section 502, with pay from the United States. U.S. Code
• Under 32 U.S.C. 502(f), a Guard member may be ordered to perform training or other duty beyond regular drills and training, and that duty may include supporting operations or missions undertaken by the member’s unit at the request of the president or the defense secretary. U.S. Code
• The duty is ordered under regulations of the Army or Air Force secretary. A member may be ordered to it without consent, but then with the pay and allowances provided by law. U.S. Code
• The president may call members and units of any state’s National Guard into federal service, in the numbers the president considers necessary, when the United States or a commonwealth or possession is invaded or in danger of invasion by a foreign nation, when there is a rebellion or danger of a rebellion against the federal government’s authority, or when the president is unable with the regular forces to execute federal law. The call is “to repel the invasion, suppress the rebellion, or execute those laws.” U.S. Code
• Orders calling the Guard into federal service under 10 U.S.C. 12406 must be issued through the states’ governors, or for the District of Columbia, through the commanding general of its National Guard. U.S. Code
• Guard members called into federal service are subject to the laws and regulations governing the Army or the Air Force from the time they are required to respond to the call. U.S. Code
• A Guard member ordered to active duty is relieved from duty in the state’s National Guard until released from active duty. An officer isn’t relieved if the president authorizes service in both statuses and the governor consents. U.S. Code
• Guard members enlist in both their state’s Guard and the National Guard of the United States, and when called to active duty in federal service, they are relieved of their state militia status. The Supreme Court has approved that system. Constitution Annotated
• The Constitution’s three purposes for calling forth the militia (executing the laws, suppressing insurrections and repelling invasions) don’t limit the federalized National Guard. Constitution Annotated
• The president is commander in chief of the states’ militia “when called into the actual Service of the United States.” Constitution Annotated
• The Posse Comitatus Act’s text names “the Army, the Navy, the Marine Corps, the Air Force, or the Space Force.” It doesn’t name the National Guard. U.S. Code
• The Army National Guard, while in the service of the United States, is a component of the Army. U.S. Code
• The Air National Guard, while in the service of the United States, is a component of the Air Force. U.S. Code

Other Laws That Authorize Troops at Home

• The FBI investigates the killing, kidnapping or assault of the president, the vice president and certain others, and it may request help from any federal, state or local agency, “including the Army, Navy, and Air Force, any statute, rule, or regulation to the contrary notwithstanding.” U.S. Code
• In an emergency involving a weapon of mass destruction, the defense secretary, at the attorney general’s request, may provide Defense Department help, including personnel, to support enforcement of certain federal weapons laws if the two jointly determine that an emergency exists and the defense secretary determines that the help won’t adversely affect U.S. military preparedness. U.S. Code
• The rules for that help may allow an arrest, or direct participation in a search or seizure of evidence, only when the action is necessary for the immediate protection of human life, civilian law enforcement officials can’t take it, and it is otherwise authorized. U.S. Code

Disasters and Emergencies

• Right after an incident that may qualify for Stafford Act disaster aid, the state’s governor may ask the president to direct the defense secretary to use Defense Department resources for emergency work essential to preserving life and property. If the president determines the work is essential, the president must grant the request to the extent the president determines practicable. The work may last no more than 10 days. U.S. Code
• Emergency work includes clearing and removing debris and wreckage and temporarily restoring essential public facilities and services. U.S. Code
• In a major disaster, federal agencies may, at the president’s direction, provide help essential to meeting immediate threats to life and property, including search and rescue, emergency medical care and shelter, debris removal and clearing roads. U.S. Code
• When a governor asks for federal help with a major disaster or emergency, the defense secretary may order Army, Navy, Marine Corps and Air Force Reserve units and members to active duty, without their consent, for up to 120 days in a row. U.S. Code

Declaring War and Authorizing Force

• An early draft of the Constitution gave Congress the power “to make war.” The Convention changed it to “declare war.” The Constitution Annotated says the change appears more likely to have been meant to ensure the president could repel sudden attacks without waiting for Congress, and to make clear that conducting war belongs to the president. Constitution Annotated
• When hostile action is taken against the nation, its citizens or its commerce, the president may use force in response. Constitution Annotated
• In the Prize Cases of 1863, a divided Supreme Court said that if a foreign nation invades, the president “is not only authorized but bound to resist force by force,” without waiting for any special authority from Congress. Constitution Annotated
• Congress doesn’t have to declare war in the all-out sense. It may provide for a limited war. Constitution Annotated
• Authority to send forces into hostilities isn’t to be inferred from any law, including an appropriations act, unless the law specifically authorizes it and states that it is intended to be specific statutory authorization under the War Powers Resolution. U.S. Code
• Nor is it to be inferred from a treaty, unless the treaty is implemented by legislation that specifically authorizes sending forces into hostilities and says it is intended to be that specific statutory authorization. U.S. Code

The War Powers Resolution

• Congress passed the War Powers Resolution over the president’s veto in 1973. Constitution Annotated
• The War Powers Resolution’s stated purpose is to ensure that “the collective judgment of both the Congress and the President” applies to sending U.S. armed forces into hostilities and to keeping them there. U.S. Code
• The resolution states that the president’s power as commander in chief to send U.S. armed forces into hostilities, or into situations where hostilities are clearly imminent, is exercised only under a declaration of war, a specific statutory authorization, or a national emergency created by an attack on the United States, its territories or possessions, or its armed forces. U.S. Code
• The president “in every possible instance” must consult Congress before sending U.S. armed forces into hostilities, and must keep consulting regularly until they are out. U.S. Code

Without a declaration of war, the president must send a written report within 48 hours to the speaker of the House and the Senate’s president pro tempore when U.S. armed forces are sent: U.S. Code

• Into hostilities, or into situations where imminent involvement in hostilities is clearly indicated by the circumstances. U.S. Code
• Into a foreign nation’s territory, airspace or waters while equipped for combat, except deployments that relate solely to supply, replacement, repair or training of those forces. U.S. Code
• In numbers that substantially enlarge U.S. forces equipped for combat already in a foreign nation. U.S. Code
• The report must set out the circumstances, the constitutional and legislative authority for sending the forces, and the estimated scope and duration of the hostilities or involvement. U.S. Code
• While the forces remain engaged, the president must report to Congress periodically, and at least once every six months. U.S. Code
• The president must also provide other information Congress requests in carrying out its constitutional responsibilities for committing the nation to war and using U.S. forces abroad. U.S. Code
• Within 60 calendar days after a report on sending forces into hostilities, or into situations where hostilities are clearly imminent, is submitted or required, whichever is earlier, the president must end that use of the forces unless Congress has declared war or enacted a specific authorization, has extended the 60 days by law, or is physically unable to meet because of an armed attack on the United States. U.S. Code
• The 60 days can be extended by no more than 30 days if the president certifies to Congress in writing that unavoidable military necessity, for the safety of U.S. forces, requires their continued use while bringing about their prompt removal. U.S. Code
• The resolution says that when U.S. forces are engaged in hostilities outside U.S. territory without a declaration of war or specific statutory authorization, the president must remove them if Congress so directs by concurrent resolution. U.S. Code
• After the Supreme Court’s 1983 decision in INS v. Chadha, Congress enacted expedited procedures for joint resolutions or bills requiring the removal of U.S. armed forces from hostilities. Constitution Annotated
• Those joint resolutions and bills, which can be amended, get expedited consideration. If the president vetoes one, Senate debate on the veto message is limited to 20 hours. U.S. Code
• The resolution says it isn’t intended to alter the constitutional authority of Congress or the president, and it grants the president no authority over sending forces into hostilities that the president wouldn’t have without it. U.S. Code
• Presidents have generally treated the resolution as at least partly an unconstitutional infringement on their powers, the Constitution Annotated says, and have filed their reports “consistent[ly] with” its reporting section rather than under it. Constitution Annotated

The Commander in Chief

• Alexander Hamilton said the office “would amount to nothing more than the supreme command and direction of the Military and naval forces, as first general and admiral of the confederacy.” Constitution Annotated
• In 1850, the Supreme Court described the president’s wartime role as “purely military”: directing “the movements of the naval and military forces placed by law at his command,” and employing them as he judges most effective against the enemy. Constitution Annotated
• In Little v. Barreme (1804), Chief Justice John Marshall held that a presidential order conflicting with a law Congress had passed was invalid. The order wasn’t given the force of law, and the ship captain who followed it could be held liable for damages. Constitution Annotated
• Four justices wrote in Ex parte Milligan (1866) that Congress’s war power reaches all legislation essential to prosecuting a war, except laws that interfere with “the command of the forces and the conduct of campaigns,” which belong to the president as commander in chief. Constitution Annotated

What Congress and the Courts Can Do

• Congress raises and supports the Army, and no money appropriated for it may be for a term longer than two years. Constitution Annotated
• The Supreme Court has described Congress’s power over the militia as “unlimited, except in the two particulars of officering and training them.” Constitution Annotated
• Because the Constitution gives Congress the job of organizing the militia, and Congress has shared it with the executive branch by law, the courts can’t oversee how the militia is organized and provided for, though wrongs committed by troops can bring damages in court. Constitution Annotated
• In Sterling v. Constantin (1932), a case about a governor’s use of military force, the Supreme Court said the allowable limits of military discretion, and whether they have been overstepped in a particular case, “are judicial questions.” Constitution Annotated
• Whether the Constitution lets the president commit troops abroad to further national interests without a declaration of war or a specific authorization from Congress has been controversial. Constitution Annotated
• As of its 2022 edition, the Constitution Annotated says the Supreme Court has not addressed that question, and lower courts have generally not decided it, treating it as a “political question.” Constitution Annotated
• Without guidance from the courts, Congress and the president have had to reach accommodations with each other. Constitution Annotated

Related GovFacts Articles

• The Insurrection Act: A President’s Power to Deploy Troops at Home
• Drawing the Line Between Soldiers and Police: Understanding the Posse Comitatus Act
• Who Controls America’s Military: Presidential vs. Congressional War Powers
• Three Hats, One Soldier: The Complex World of National Guard Duty Status