Explainer: Why the “casual invocation” of the Insurrection Act by President Trump is so unusual

A little-used federal law is getting quite a bit of attention in the Trump administration.  

The Insurrection Act, first enacted in 1807, allows the president to deploy the United States military and federalize National Guard units in states. The circumstances requiring the Insurrection Act to be invoked are clear: to respond to a request by a state’s governing body; to address an insurrection in any state that prevents enforcement of a federal law; to address actions that result in the deprivation of constitutional rights. However, what defines civil disorder, insurrection, or rebellion is vague. 

President Trump has threatened to invoke the act twice: once in his first term during the 2020 George Floyd protests and more recently, in 2025, during the ICE protests in Los Angeles. Both times he was convinced not to do so.  

HKS talked to former assistant secretary for intergovernmental affairs at the Department of Homeland Security, Juliette Kayyem, to learn more about the Insurrection Act, how it is used, and what it means to the current administration.  

Kayyem is the Robert and Renee Belfer Senior Lecturer and faculty chair of the Homeland Security and Security and Global Health Projects at Harvard Kennedy School.

Q: What is the Insurrection Act?

The Insurrection Act is authorized by the insurrection provision of the Constitution, which basically says the president can call forth the militia in an insurrection. But insurrection is not defined.

The act itself tries to define the term, but its language is not clear because civil unrest, an inability to execute the law, is very, very vague.

What people need to understand is that it is used to get around the Posse Comitatus Act passed after the Civil War, which prohibits the military from being utilized for law enforcement purposes.

The Posse Comitatus Act says if you use the military in the United States for, say, a disaster, they cannot have law enforcement functions. They essentially cannot arrest.

The Insurrection Act basically says the president can use the military for law enforcement purposes. That is a use of the military that has never been part of the way we think about ourselves.

Q: How has the Insurrection Act been used before?

Since its inception, fifteen presidents have used it. In modern times, presidents used it during the civil rights era when governors in some states were ignoring the Supreme Court rulings on desegregation. It was used again in 1992 to quell riots following the Rodney King verdict, at the request of California Governor Pete Wilson.  

During Hurricane Katrina, again the governor of Louisiana asked. Interestingly enough, President Bush did not invoke the Insurrection Act. He believed the military was better suited in its support function, rather than overwhelming civil society.

It is important to understand that it has been used, but presidents have used it in very different circumstances than the way Trump is thinking. If Hurricane Katrina is your benchmark for deployment, then the perception of rising crime rates in New York, Boston, or Los Angeles doesn’t meet the mark.

Q: How is this administration thinking about the Insurrection Act?

My understanding is that Secretary of Defense Pete Hegseth would be prepared to deploy the military, as a law enforcement entity, in a number of cities, most of them in blue states, where there is a perception of high crime. President Trump campaigned on lower crime in our cities.  

There is a sentiment in the Pentagon that employees are nervous because they were raised not to go to war with us, with civilians. That’s how they are trained. That is how they understand the mission.  

And I want to clear about this: the military is totally integrated in supporting communities when they need them. Whether it was Hurricane Katrina or during an Olympics, they are there. The idea that their vast resources aren’t used is a misunderstanding of how the local, state, and federal capacity is aligned.

What we saw with the National Guard in D.C. illustrated this. An insurrection means state government can’t work; that’s the way it is defined in the Insurrection Act. And yet federal troops were deployed, and what did they do? They picked up trash. It is so expensive to deploy the military in this way. There is now a sense that this expansive definition of an insurrection could extend to the mid-term elections, where this administration can deploy the military to cities simply to intimidate voting.

This president would use the Insurrection Act in a disruptive and antagonistic way against communities and local leadership.

Q: The riot at the Capitol on January 6 has been called an insurrection. Why do you think it wasn’t invoked then when Trump was president?

He did not invoke it, and we now know from the January 6th commission, that he spent hours talking about the riots on social media before he was finally convinced to address them. Now we have seen him give pardons to people convicted during the insurrection. It is clear; he believes an insurrection only exists if it prevents his retention of power.

When I look at what makes American democracy unique, it our constitutional structure that has a clear division between civilian authorities and military authorities.

Trump’s casual invocation of the Insurrection Act is very unique for a number of reasons. Under no circumstances could you call the crime rate in our cities an “insurrection” as it is understood in the Insurrection Act. He uses it to assert executive power over states, against the consent of a governor.

We have a president who wants to use the military as an extension of law enforcement. That’s a significant change. And we should be wary about this sort of casualness in which he disrupts that constitutional order.