Protecting the Integrity of the National Guard

Claire Finkelstein is the Algernon Biddle professor of law and professor of philosophy at the University of Pennsylvania, where she is the faculty director of the Center for Ethics and the Rule of Law.

Posse comitatus, which is both a general principle and a criminal statute enshrined in the Posse Comitatus Act (PCA), dictates that there should be a clear separation between military and law enforcement. In a handful of incidents in U.S. history, the National Guard has been called out to address civilian unrest, and in such instances they are often called out in their federalized capacity. Famous instances in which a president has federalized the National Guard include when President Dwight D. Eisenhower federalized the Arkansas National Guard to enforce the school integration decision in Brown v. Board of Education and when President H. W. Bush called up the Guard to suppress riots in Los Angeles following the Rodney King verdict in 1992. Yet National Guard troops are rarely federalized. They have traditionally remained under the control of state governors, particularly insofar as they are not called out to assist with law enforcement activities, either under State Active Duty status or under Title 32. Posse comitatus does not apply when the Guard is called up in either of its state-led capacities.

By contrast, when the National Guard is called up by the U.S. president under Title 10 and thus federalized, posse comitatus applies. This gives the federal government every incentive to attempt to deploy the Guard in its state capacity—under either its State Active Duty or Title 32 status.

Agreements recently reached between the Trump administration and the Texas and Florida National Guards clearly demonstrate the complexities of National Guard authority and the risk of federalization. The Trump administration wants state governors to dedicate their National Guard units to Customs and Border Patrol (CBP) and to U.S. Immigration and Customs Enforcement (ICE) efforts to round up large numbers of undocumented immigrants in the United States. The agreement between the Florida State Guard and ICE, for example, uses the authority of 287(g) of the Immigration and Nationality Act to allow federal officials to designate Guardsmen as law enforcement officers. The comparable agreement in Texas uses the Mass Influx finding to grant Texas National Guard personnel the ability to exercise the duties and functions of immigration officers “under the supervision and direction of CBP officials.” Under both agreements, Guard personnel would be tasked with conducting arrests, rounding up illegal immigrants, or persons rendered illegal by having their visa cancelled by CBP, and possibly presiding over mass detention facilities of unlawful aliens who are awaiting questioning or deportation by CBP officials.

Some state governors have refused the federal demand to turn over their National Guard to Trump’s mass immigration project. Gov. Michelle Lujan Grisham of New Mexico, for example, refused, following which she declared a crime emergency in New Mexico and deployed the Guard to assist with crime control, including directing traffic. Deploying the state’s National Guard elsewhere presumably helps Gov. Grisham resist Trump’s demand to deploy the Guard in aid of the planned immigration roundups—a major undertaking in a border state like New Mexico and one that would presumably be deeply controversial in that state. The state of Washington went further and signed a bill into law forbidding out-of-state forces from entering Washington without the governor’s permission. Upon signing the bill, Washington’s Governor Bob Ferguson said, “We cannot have armed forces come into our state to enforce policies that are against our core values.” This raises the question as to President Trump’s legal options for forcing compliance and state governors’ options to fight back.

A Tradition Against Military Engagement in Law Enforcement

An important exception to the applicability of posse comitatus to the Guard in federalized status may make state resistance more challenging. The Insurrection Act permits the president to deploy the military to suppress an insurrection or otherwise enforce the law when other means of ensuring legal compliance are unavailable. Federalizing a state’s National Guard under the Insurrection Act allows a president to exert maximum control over National Guard troops. Black letter law suggests that invoking the Insurrection Act renders posse comitatus constraints entirely inapplicable. Of all the contexts in which posse comitatus may be threatened, the Insurrection Act presents a worst-case scenario, but the precise relationship between the Insurrection Act and the general principle of posse comitatus has rarely been tested in a court of law.

Could a governor or other state official challenge the federal government in an Article III court for improper use of the Insurrection Act? There are few decided cases, but two arguably bear on this question. The 19th-century case Martin v. Mott suggests that a presidential order issued under the Insurrection Act would be entirely nonjusticiable, while an early 20th-century case, Sterling v. Constantin, takes a different view in a suit against state officials and the adjutant general (the head of the state National Guard) rather than against federal government officials. It thus remains unclear whether a suit to address the potentially limited nature of the suspension of posse comitatus upon invocation of the Insurrection Act would fail on justiciability grounds.

Even where invocation of the Insurrection Act is legal, it is not clear how far military commanders are likely to press the boundaries of posse comitatus. Military leaders do not want their troops to engage in acts typically conducted by law enforcement officers, and troops are not generally trained to carry out such missions. Indeed, the author’s center, the Center for Ethics and the Rule of Law, conducted an initial pilot survey of 30 ROTC cadets, asking them to assess the accuracy of the statement that “under U.S. law, the president is prohibited from using the military as a domestic police force.” The survey found that 38.5 percent of participants found this characterization “very accurate” and 30.8 percent of participants found this statement “somewhat accurate.” Together, nearly 70 percent of survey participants were of the view that the president lacks the power to use the military as a domestic police force. While the sample size of the pilot study is too small to be probative, if the results of a wider survey match the pilot test, they will strongly support the general observation that posse comitatus goes beyond the narrow strictures of the PCA: it is a general military ethos that characterizes how military officials see the proper role of troops and the boundaries on the tasks to which they can be assigned.

Criminal Enforcement of the PCA Is an Insufficient Check on Authority

The PCA itself is framed as a criminal statute. Thus, the effectiveness of the act depends on an ancillary ability of the government to prosecute an official for a criminal act. Successful prosecution of a president or member of the president’s cabinet is unlikely under the Supreme Court’s 2024 immunity decision in Trump v. United States, which grants a president immunity from criminal charges for official acts. As explained in the amicus brief this author filed, along with 14 senior national security leaders in that case, any orders for domestic troops to engage in domestic law enforcement activities would, without question, constitute official capacity acts. Furthermore, three Department of Justice memos from the Office of Legal Counsel also say that a sitting president cannot be indicted, even for personal capacity crimes. Justice John Roberts was not clear in the immunity decision how far presidential immunity would extend down the chain of command, and thus this question of the immunity of subordinate cabinet officers was left unresolved. But if criminal immunity were extended to the secretary of defense, it would be unlikely to extend all the way down to lower-level military officers. A subordinate military officer could almost certainly be prosecuted for posse comitatus violations even if the ultimate commander could not be.

In any event, even if lower-level officers in the military chain of command could be prosecuted for PCA violations, their prosecution would require the cooperation of either the Department of Justice or the Department of Defense, both unlikely scenarios under present circumstances. Thus, it seems unlikely that reluctant governors could protect their control over the Guard by attempting to bring a federal case against military commanders for PCA violations.

Enforcing Posse Comitatus Through State Action

State law reform efforts present an alternative approach to invoking the criminal penalties of the PCA. State legislators, for example, could pass laws equipping state actors with the right to sue on violations of the PCA. After all, in a case in which the state had not requested federal involvement, a state legislature might wish to protect the state’s autonomy by pushing back against violations of a governor’s control of the state’s National Guard.

Alternatively, as discussed above in connection with the State of Washington, state legislatures can pass legislation forbidding the use of the state National Guard for law enforcement purposes without permission of the governor. This would not protect against federalization, which is controlled by federal, not state, law. But since federalization implicates posse comitatus in any event, such laws would at least prohibit the use of national guard troops for law enforcement purposes when the Guard was serving in its nonfederalized capacities.

A state statute bolstering the ability of a governor to oppose incursions of the federal government into state control over its National Guard would likely be enforceable. State passage of implementing legislation designed to support federal law is routine and has been ruled constitutional in U.S. federal courts. For example, states have long passed state laws designed to ensure compliance with federal civil rights laws.

Additionally, states can mandate basic training of its own National Guard and the rule-of-law instruction of its troops. Such training has presumably played a greater role in sustaining the commitment to avoiding the involvement of the U.S. military in law enforcement matters than has the threat of prosecution under the PCA itself. The commitment of the principle of posse comitatus with the U.S. military stems from respect for democratic governance and understanding of the civilian–military divide that has helped to differentiate the function of U.S. military troops from their civilian counterparts in both federal and state governments for most of U.S. history.

About the Commentary Series

In February 2024, the Center for a New American Security (CNAS) launched a project on federalism and national security. This portfolio has taken shape under the CNAS Securing U.S. Democracy Initiative. Recognizing that the 21st-century United States increasingly relies on its system of federalism to rebalance the centers of power and authority across a range of public policy issues, the Securing Democracy Initiative has developed a body of work focused on states’ authorities, roles, and responsibilities that relate to national security functions. Increasing reliance on the U.S. federalist system of government presents both challenges and opportunities for strengthening national security. This commentary series and the December 2024 report Stress Testing State Power: When Governors and Presidents Diverge on Matters of National Security are components of this research effort.

Each commentary in this series explores a current trend or dynamic in modern uses and authorities of the National Guard. Expert authors explore how the Guard is currently being used and will be increasingly called upon in years ahead. Authors provide recommendations for modernizing and clarifying legal authorities for National Guard deployment, and for legislative action at the state and federal levels.

The CNAS project on federalism and national security is made possible with the generous support of the Democracy Innovation Fund, Defending Democracy Together Institute. As a research and policy institution committed to the highest standards of organizational, intellectual, and personal integrity, CNAS maintains strict intellectual independence and sole editorial direction and control over its ideas, projects, publications, events, and other research activities. CNAS does not take institutional positions on policy issues, and the content of CNAS publications reflects the views of their authors alone. In keeping with its mission and values, CNAS does not engage in lobbying activity and complies fully with all applicable federal, state, and local laws. CNAS will not engage in any representational activities or advocacy on behalf of any entities or interests and, to the extent that the Center accepts funding from non-U.S. sources, its activities will be limited to bona fide scholastic, academic, and research-related activities, consistent with applicable federal law. The Center publicly acknowledges on its website annually all donors who contribute.