Since January 6, roughly 2,000 ICE agents have been deployed to Minnesota under the pretext of responding to a fraud investigation. In practice, these largely untrained and undisciplined federal agents have been terrorizing Minneapolis residents through illegal and excessive uses of force – often against US citizens – prompting a federal judge to attempt to place limits on the agency’s actions. The Trump administration is encouraging the lawlessness by announcing “absolute immunity” for ICE agents. But if the secretary of homeland security, Kristi Noem, does not heed the court ruling, the consequences may be nothing short of civil war.

In just the past week, ICE agents shot and killed Renee Good, a 37-year-old mother of three, shortly after she returned from dropping her child off at school. They blinded two protesters by shooting them in the face with so-called “less deadly” weapons. They fired teargas bombs around the car of a family carrying six children, sending one child to the emergency room with breathing problems. They violently dragged a woman out of her car and on to the ground screaming. They have shot protesters in the legs. They have forcibly taken thousands of individuals to detention facilities, separating families and casting people into legal limbo – often without regard to their legal status.

Rather than investigate this conduct and the officer who shot Renee Good, the justice department has opened a criminal investigation into the Minnesota governor, Tim Walz, and Minneapolis mayor, Jacob Frey, accusing them of conspiring to impede federal agents. Renee Good’s widow is also under investigation, a move that prompted six US attorneys in Minnesota to resign in protest.

As public outrage grows, ICE has escalated its actions, increasingly engaging in what appear to be random acts of violence regardless of immigration status. Governor Walz has placed the Minnesota national guard on standby to support local law enforcement, while Trump has threatened to invoke the Insurrection Act – an extraordinary move that would grant him sweeping domestic military powers and potentially sidestep recent supreme court limits on the use of federal troops in law enforcement. One thousand additional ICE agents have been sent to Minnesota, suggesting that Trump is essentially using ICE as a specialized paramilitary force to target protesters and suppress dissent. And the Pentagon has readied the army’s 11th Airborne Division – roughly 1,500 active-duty soldiers – to back up the president’s threat.

This scenario closely mirrors one explored in an October 2024 tabletop exercise conducted by the Center for Ethics and the Rule of Law (CERL), which I direct, at the University of Pennsylvania. In that exercise, a president carried out a highly unpopular law-enforcement operation in Philadelphia and attempted to federalize the Pennsylvania’s national guard. When the governor resisted and the guard remained loyal to the state, the president deployed active-duty troops, resulting in an armed conflict between state and federal forces. While the location and sequence differ, the core danger we identified is now emerging: a violent confrontation between state and federal military forces in a major American city.

While our hypothetical scenario picked a different city and a slightly different sequence of events, the conclusions we reached about the possibility of green-on-green violence are directly applicable to the current situation. First, none of the participants – many of them senior former military and government officials – considered the scenario unrealistic, especially after the supreme court’s decision in Trump v United States, which granted the president criminal immunity for official acts.

Second, we concluded that in a fast-moving emergency of this magnitude, courts would probably be unable or unwilling to intervene in time, leaving state officials without meaningful judicial relief. State officials might file emergency motions to enjoin the use of federal troops, but judges would either fail to respond quickly enough or decline to rule on what they view as a “political question”, leaving the conflict unresolved. This is why Judge Menendez’s ruling is so critical: it may be the last opportunity a federal judge has to intervene before matters spiral completely out of control.

Third, we warned that senior military leaders could face orders to use force not only against state national guard units, but against unarmed civilians – and that they must be prepared to assess the legality of such orders. Any domestic deployment of federal troops must comply with the Department of Defense’s Rules for the Use of Force and with the constitution, including the Bill of Rights. Even under the Insurrection Act, federal troops may not lawfully shoot protesters unless they are literally defending their lives against an imminent threat – yet such conduct is already happening in Minneapolis at the hands of federal agents.

Finally, it is not legal for federal troops to back up ICE agents who are behaving illegally.

Every member of the US military has sworn an oath to defend the constitution. That oath carries legal force. Service members are not only permitted but obligated to refuse patently illegal orders.

That obligation is now under pressure. Senator Mark Kelly is under investigation by the Pentagon for publicly reminding service members in a video he made with five other members of Congress that they may – and in some cases must – refuse illegal orders. But they were essentially correct: troops must refuse to carry out patently illegal orders.

For members of the 11th Airborne Division, this may soon cease to be a theoretical question. Minnesota may be the first test of whether constitutional limits on domestic military force still hold – or whether the United States is about to cross a line from which it cannot easily return.