Learn about the story, Federalized National Guard Troops, The Posse Comitatus Act, and The Insurrection Act from FindLaw.com, along with reading the article, What is the Insurrection Act? Does the US president have plenary authority?, from Politifact.

According to the article, when asked whether President Donald Trump would invoke the Insurrection Act, Vice President J.D. Vance said Trump is "looking at all his options."

The decision would allow Trump to deploy the U.S. military domestically for law enforcement purposes without congressional authorization and over the objections of state governors.

Vance’s October 12 comment  was just one of many in recent months about Trump’s ambitions to send the National Guard to Democratic cities such as Portland and Chicago.

But the legal terms being tossed around — the Insurrection Act, plenary authority, martial law, and the Posse Comitatus Act — might not be familiar to everyone. These terms defy simple definitions after decades of interpretation by the courts. 

What is the Insurrection Act?

This 1807 law allows the U.S. president to deploy federal military personnel domestically to suppress rebellion and enforce civilian law.

Invoking the Insurrection Act temporarily suspends another U.S. law that forbids federal troops from conducting civilian law enforcement. A president can invoke the law after determining that "unlawful obstructions, combinations, or assemblages, or rebellion" against the federal government make it "impracticable to enforce" U.S. law "by the ordinary course of judicial proceedings," the law says. In those cases, the Insurrection Act would allow the president to direct federal troops to enforce U.S. laws or stop a rebellion.

The law is broadly written and doesn’t define terms such as "insurrection" or "rebellion." The U.S. Supreme Court ruled in 1827 that the president has exclusive power to decide whether a situation represents an acceptable reason to invoke the law.

Chris Edelson, an American University assistant professor of government, said the law provides "limited authority" for the president to use the military to respond to "genuine emergencies — a breakdown in regular operational law when things are really falling apart."

The Insurrection Act has been formally invoked around 30 times in the U.S. since 1808, including when southern governors refused to integrate schools in the 1950s and ’60s and during the 1992 Los Angeles riots, after four white police officers were acquitted in the roadside beating of Rodney King, a Black man.

What is Martial Law?

People sometimes conflate martial law with the Insurrection Act. Martial law typically refers to imposing military law on civilians, while the Insurrection Act uses the military to impose civilian law. Martial law is more stringent and has fewer protections than civilian law, experts said.

The Supreme Court wrote in a 1946 ruling that the term martial law "carries no precise meaning," and that it was not defined in the Constitution or in an act of Congress. Legal experts said that because of this, it is not clear whether the U.S. president has a legal path to declaring martial law in the way that it’s commonly understood.

Still, it has been declared in the past. The U.S. imposed martial law in Hawaii after the 1941 Japanese attack on Pearl Harbor, and President Abraham Lincoln declared martial law in certain parts of the country during the Civil War.

The Supreme Court held in 1866 that martial law could be imposed only if civilian courts weren’t functioning.

The court "more or less found that martial law could only be declared in an active war zone," Chris Mirasola, University of Houston Law Center assistant professor, said. "The circumstances within which presidents have invoked martial law and that the Supreme Court has understood martial law are incredibly narrow. It would require an active hostility on U.S. territory that prevents civilian legal proceedings from occurring."

Trump, who has shown a willingness to challenge constitutional precedent, has continued to muse about using military powers against civilians. Trump told top U.S. military commanders Sept. 30 that the military could be used against the "enemy within" and suggested that some U.S. cities could be used as military "training grounds."

What Is Plenary Authority?

"Plenary authority" is defined by the Legal Information Institute at Cornell Law School as "power that is wide-ranging, broadly construed, and often limitless for all practical purposes."

The term made headlines when White House Deputy Chief of Staff Stephen Miller started to say that Trump has "plenary authority" to deploy National Guard troops to U.S. cities in an October 6 interview. Miller abruptly stopped talking and the media said the disruption was from a technical glitch. But social media users said Miller froze because he mentioned plenary authority.

When the show returned, Miller finished his answer, saying he was "making the point that under federal law, Title 10 of the U.S. Code, the president has the authority anytime he believes federal resources are insufficient to federalize the National Guard to carry out a mission necessary for public safety."

Although the president has broad powers under the Constitution, like issuing pardons for federal crimes, he does not have limitless power. The U.S. government is divided into three branches — legislative, executive and judicial — in order to have checks and balances.

Title 10 of the U.S. code outlines the role of the country's armed forces and constrains what the military is allowed to do and what orders the president can lawfully issue.

It does not include terms like "plenary authority" or "plenary power." Instead, it says that when the president "is unable with the regular forces to execute the laws of the United States" and the U.S. faces a foreign invasion, a rebellion, or danger of rebellion, the president "may call into Federal service members and units of the National Guard of any state." 

A judge in Oregon has twice blocked the Trump administration from deploying National Guard troops to Portland; a federal appeals court also blocked the administration from deploying the guard to Chicago, saying troops can remain federalized for now but cannot be deployed.

Trump officials say the guard is needed to protect federal ICE officers and federal facilities. Trump previously cited section 12406 of Title 10 when he called for National Guard troops to be sent to Los Angeles during immigration protests in June. A federal judge ruled in September the deployment violated the law. The administration is appealing.

What is the Posse Comitatus Act?

The Posse Comitatus Act, passed in 1878, generally prevents the use of the military as a domestic police force on U.S. soil, with exceptions for the Insurrection Act

.The phrase "posse comitatus" refers to a group of people called upon by a county sheriff to maintain peace and suppress lawlessness. Think of Western movie depictions of posses of townspeople gathering to catch fugitives. "The Posse Comitatus Act is so named because one of the things it prohibits is using soldiers rather than civilians as a posse comitatus," the Brennan Center for Justice, a progressive nonprofit policy institute, wrote in 2021.

As the Posse Comitatus Act has been interpreted by the courts, civilian law-enforcement officials cannot make "direct active use" of military personnel, including using federal military forces, over their citizens to "regulatory, prescriptive, or compulsory authority," according to the Congressional Research Service.

The Posse Comitatus Act does not apply to the National Guard when it is under state authority and the command of a governor; the law’s restrictions apply when the National Guard is federalized by the president. This means the National Guard generally cannot conduct arrests, searches or seizures unless there is an exception, such as the Insurrection Act.

The only National Guard exception is the District of Columbia’s, which is solely under federal control. 

What is the National Guard?

The National Guard is a state-based military force with certain federal responsibilities. The guard often responds to domestic emergencies, such as natural disasters and civil unrest, and can support U.S. military operations overseas.

Over 430,000 National Guard members serve in units in all 50 states, the District of Columbia, and the U.S. territories of Guam, Puerto Rico and the U.S. Virgin Islands.

The National Guard typically operates as a part-time reserve force that can be mobilized for active duty by governors. The guard also helps train foreign allies in over 100 countries under the State Partnership Program.

A president in some cases can federalize and take control of a state’s National Guard over the objection of governors for domestic missions and to serve in wars overseas, but it rarely happens without governors’ consent. When the National Guard is federalized, its troops are subject to the same restrictions as federal troops.

The National Guard has been federally mobilized in the U.S. several times, including in response to the 2020 protests over the murder of George Floyd; the 1992 Los Angeles riots; and civil unrest following the 1968 assassination of Martin Luther King, Jr.

The Ohio National Guard’s 1970 deployment to anti-war protests at Kent State University resulted in troops shooting students, killing four people and injuring nine others.

Explaining the Two Historical Acts in the National Guard Controversy

Further understanding of the challenges and controversy on Trump's use of the National Guard 8s available from the Constitution Center.

According to the article, as the battle over the Trump administration’s use of National Guard troops to protect immigration enforcement officials plays out in the legal system, some formerly obscure acts of Congress could play a key role in the appeals process.

Recently, Judge April M. Perry of the United States District Court of the Northern District of Illinois issued a temporary restraining order against the deployment of troops in Illinois. Perry had heard arguments during the day in a lawsuit asking the court to bar the National Guard from Chicago, in part citing violations of the Posse Comitatus Act of 1878.

Also, in public statements, President Donald Trump has stated he might invoke the Insurrection Act of 1807 to use military forces such as the National Guard in a limited fashion in domestic circumstances.

The U.S. Circuit Court of Appeals for the Ninth Circuit also recently heard arguments over whether the administration could deploy Oregon National Guard troops. In court papers, government attorneys argued that the president has the power under 10 U.S.C. § 12406, to federalize the National Guard.

A Tale of Two Acts and Two Statutes

The Posse Comitatus Act dates back to when federal troops left formerly rebellious states as part of the pact that ended a key phase of the Reconstruction in the1870s. The act was originally intended to make it difficult for federal forces to execute criminal laws in those southern states, as they had between 1865 and 1878.

In the period after the Civil War, federal troops in the former states of the Confederacy were used to enforce laws. The ex-Confederate states strongly opposed this policy. As explained in a 2018 report from the Congressional Research Service, the Posse Comitatus Act outlawed the willful use of any part of the Army or Air Force as a “posse comitatus” to execute the law unless expressly authorized by the Constitution or an act of Congress.

Violations of the Posse Comitatus Act occur when federal forces take over tasks assigned to a civil government, or when federal armed forces perform tasks solely for purposes of civilian government. Also, civilian law enforcement is barred from “direct active use” of military investigators, and the use of the military cannot “pervade the activities of the civilian officials.”

According to the CRS, clear exceptions to the Posse Comitatus Act exist where “Congress has delegated authority to the president to call forth the military during an insurrection or civil disturbance.”

Another statute, Section 502 of Title 32, U.S. Code, permits the use of the National Guard if it takes part in “homeland defense activity” that is “undertaken for the military protection of the territory or domestic population of the United States, or of infrastructure or other assets of the United States determined by the Secretary of Defense as being critical to national security, from a threat or aggression against the United States.”

The statute cited in the Oregon case, 10 U.S.C. § 12406, was used by the administration to justify the use of National Guard troops in California. It allows the president to federalize the National Guard if the United States is invaded or is in danger of invasion by a foreign nation; there is a rebellion or danger of a rebellion against the authority of the government of the United States; or the president is unable with the regular forces to execute the laws of the United States.

The Insurrection Act of 1807 is one of a series of laws that Congress has passed to allow the president to deploy the National Guard or federal armed forces to deal with “unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States.”

The last use of the Insurrection Act was in May 1992, when President George H.W. Bush directed the use of 3,500 federal troops after California’s governor requested help when the National Guard could not contain riots related to the Rodney King case. In 1957, President Dwight D. Eisenhower sent federal soldiers under another statute to enforce the desegregation at Central High School in Little Rock, Arkansas.

The Militia Clauses

The founders had firsthand experience with the need to contain public disturbances in limited circumstances. The Articles of Confederation, which preceded the Constitution, lacked the power to initially deal with Shays’ Rebellion in 1786. At the Constitutional Convention in Philadelphia in 1787, the delegates sought to balance the need for stronger militias and a federal military force, with their fear of a standing army that might abuse its powers.

The Constitution gave overlapping powers to civilians to oversee military forces. Article I, Section 8, called for Congress “to provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions” and “To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively.” Article II, Section 2, established that the “President shall be 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.”

The Constitution’s Article IV, Section 4, also made it clear that the federal government had a responsibility to protect states against “Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.”

After the Constitution was ratified, Congress granted the president additional powers under the Militia Act of 1792 to temporarily “call forth such number of the militia of the state or states” at the request of state leaders. The Militia Act of 1795 gave the president more powers to call out the militia by eliminating time limits for their use in the field and removing the required consent of a federal judge before taking action to call out troops.

Discussion Questions

  1. Define the following terms: (a) The Insurrection Act; (b) martial law; (c) plenary authority; and (d) The Posse Comitatus Act.

    The Insurrection Act is a federal law in the United States that gives the U.S. president the authority to deploy U.S. armed forces and National Guard units within the country to suppress civil disorder, insurrection, or rebellion. The president may invoke the Insurrection Act in three main scenarios:

    (a) If a state government asks for federal help to suppress an insurrection against its authority;
    (b) When unlawful actions prevent the enforcement of federal law in a state, and local authorities cannot or will not act; or
    (c) If there is an insurrection or domestic violence that deprives people of constitutional rights, and state authorities fail to protect them.

    The Insurrection Act’s purpose is to ensure the continuity of government, enforce federal laws, or protect civil rights when local and state governments are unable or unwilling to do so.

    Martial law is the temporary replacement of civilian authority with military authority, usually during times of war, rebellion, or extreme civil unrest, when normal civil government and law enforcement are unable to maintain order.

    In terms of the key characteristics of martial law, civilian courts may be suspended, and military tribunals may be used. Curfews, restrictions on movement, and warrantless searches may be enforced. Freedom of assembly, speech, and other civil liberties can be limited. Finally, civil authorities (e.g., the police or local government) may be replaced or controlled by military forces.

    Plenary authority (here, in the context of executive, or U.S. presidential, authority) means the full and complete power to act, without needing approval or permission from another body (e.g., the U.S. Congress), and often not subject to judicial review unless limited by a higher legal authority (e.g., the U.S. Constitution).

    The Posse Comitatus Act is a federal law that restricts the use of the U.S. military in domestic law enforcement activities, except where expressly authorized by the U.S. Constitution or an act of Congress.

  2. In your reasoned opinion, and based on the circumstances described in Video 1 and its accompanying material, does President Trump have the constitutional and/or other legal authority to deploy the National Guard to cities like Washington, D.C., Los Angeles, Portland, Chicago, etc.? Why or why not?

    This is, in some respects, an opinion question, so student responses may vary. On October 20, 2025, a federal appeals court permitted President Donald Trump to federalize and deploy the Oregon National Guard into what he is calling “war-ravaged” Portland.

    The 2-1 ruling by a three-judge panel on the U.S. Court of Appeals for the Ninth Circuit reversed a temporary restraining order that blocked the troops, as the administration challenges a lawsuit filed by Oregon and Portland officials. The case is scheduled for trial on October 29.

    In your author’s opinion, regardless of the outcome of the October 29 trial, this case must make its way to the U.S. Supreme Court for review. This is a defining moment in our country regarding the balance of power among the three branches of the federal government.

  3. In answering Video 1, Discussion Question 2 above, should it matter whether the mayor of a particular city requests the presence of the National Guard? Why or why not?
    As mentioned in response to Video 1, Discussion Question 1 above, the U.S. president may invoke the Insurrection Act in three main scenarios:

    (a) If a state government asks for federal help to suppress an insurrection against its authority;
    (b) When unlawful actions prevent the enforcement of federal law in a state, and local authorities cannot or will not act; or
    (c) If there is an insurrection or domestic violence that deprives people of constitutional rights, and state authorities fail to protect them.

    Note that only one of these scenarios (the first one) addresses a situation in which a state government asks for federal help to suppress an insurrection against its authority. No city or state has requested such assistance.

    In terms of the third scenario, the key question is whether there is an “insurrection or domestic violence that deprives people of constitutional rights.” Insurrection is a legal and political term that refers to a violent uprising or rebellion against an established government or authority. It typically involves organized resistance, such as taking up arms, disrupting government functions, or attempting to overthrow lawful authority. Your author is not aware of any “violent uprising or rebellion” that would rise to the level of insurrection. Certainly, there have been organized protests in cities like Washington, D.C., Los Angeles, Portland, and Chicago, but there is a marked distinction between the exercise of First Amendment (to the U.S. Constitution) free speech rights (particularly when it comes to political speech) and an insurrection.

    This leaves for consideration the second scenario for invoking the Insurrection Act: When unlawful actions prevent the enforcement of federal law in a state, and local authorities cannot or will not act. Presumably, the Trump administration will argue that Portland is preventing (either through its action or its inaction) the enforcement of federal immigration law. In your author’s opinion, this is the Trump administration’s best argument for invoking the Insurrection Act; however, the administration has the burden of proving at trial, based on a preponderance of the evidence, that Portland’s mis-, mal-, or nonfeasance is factual.