What history—and the law—teach us about using the military to police U.S. cities.

In recent months, talk of sending National Guard troops or even federalized forces into cities like Chicago or Portland has moved from speculation to action. Supporters say it will protect federal property and calm unrest. Critics warn it may erode the line between military and civilian law enforcement. We should look at the laws, the history, and what this could mean for our future.

Laws and limits: Posse Comitatus, Insurrection Act, and precedent

The United States has long drawn a strong line between military and police roles. The Posse Comitatus Act of 1878 generally prohibits use of federal troops to enforce domestic law unless Congress expressly allows it.  Under this law, when National Guard or military forces operate on U.S. soil under federal command (Title 10), they can’t perform arrests, searches, or seizures in civilian settings. 

One key exception is the Insurrection Act (10 U.S.C. § 251, etc.), which lets the president call up forces to suppress insurrections, enforce federal law, or protect civil rights when states cannot or will not act.  But the Insurrection Act has clear conditions and is not a free pass for broad domestic military rule. 

Legal scholars caution that a president cannot unilaterally deploy troops over the objections of a state government, in peaceful settings, or for general policing goals—that would violate both statutory limits and constitutional federalism.  A 2020 legal brief argued that deploying military forces on city streets over state objections, unrelated to civil rights enforcement or court order, lacks legal basis. 

Another tool is the Military Cooperation with Civilian Law Enforcement Agencies Act (MCCLEAA) of 1981, which allows limited support—for example equipment, intelligence, logistics—but always under constraints and not direct law enforcement by troops. 

So legally, putting soldiers on streets is possible only in narrow, controlled circumstances—and usually as backup, not front-line policing.

Recent moves: Chicago, Portland, and courtroom pushback

It’s not just theory. The Trump administration has pushed to deploy National Guard or federal troops in cities like Chicago and Portland. In Chicago, reports say about 500 National Guard troops have been activated to protect federal personnel and property, despite objections from Illinois and Chicago officials who call it unconstitutional overreach.  Illinois has filed suit to block deployment under 10 U.S.C. § 12406 and the Posse Comitatus Act. 

In Portland, a federal judge temporarily blocked deployment of 200 Oregon National Guard troops, writing that protests were too minor to justify military involvement and that the state’s sovereignty must be respected.  This ruling came from Judge Karin Immergut, a Trump appointee.  The administration has appealed. 

White House Press Secretary Karoline Leavitt defended the deployments, accusing “anarchists” of targeting ICE facilities and saying her office saw a “guillotine rolled out in front of this federal building.”  Her framing signals a hard posture toward dissent. Critics argue it helps cast political opposition as disorder.

These battles are more than about city safety—they’re tests of constitutional limits, the balance of state and federal power, and where we draw the line between security and militarized governance.

Lessons from history & what this means ahead

Looking back, domestic military deployments in U.S. cities are rare and controversial. Troops were used during Reconstruction, in race riots, or during insurrections (e.g. Pullman Strike of 1894, 1968 riots).  But over the past decades, domestic military use has been tightly limited—military roles are usually support or disaster relief, not regular patrol. 

Two major risks stand out:

1. Erosion of civil authority
   If the military steps in too often, public confidence in civilian police and local government could erode. People may come to see law enforcement as an extension of national command. That trend is worrying.
2. Precedent for more deployments
   Once militarized deployments become normal in one city, it becomes easier to argue for them elsewhere. The operational and legal boundaries may blur. Over time, that could reshape our idea of domestic public safety.

Going forward, we must watch how courts rule, how states resist or comply, and how Congress acts to safeguard limits. Legislatures could tighten or expand laws like the Insurrection Act or clarify Posse Comitatus boundaries. And public oversight must stay sharp.

A cautious path forward

Allowing National Guard or military forces into U.S. cities is not automatically wrong—but it must be done carefully, with transparency, and within clear legal guardrails. We must insist:

• Clear facts and thresholds before deployment (protests must truly threaten federal property or life, not just political messaging).
• Judicial review must be swift and meaningful. Courts should not rubber-stamp overspending or pretextual uses.
• Congressional checks and laws should be updated so authority is not bent by executive ambition.
• State and local governments must retain voice and control over policing in their communities.

If we relax the boundaries now, we risk a future where cities become zones of military presence rather than places where citizens see themselves protected under one law under civilian governance. The stakes are high.