Members of the Texas National Guard are seen at the Elwood Army Reserve Training Center on Oct. 7, 2025 in Elwood, Illinois. (Photo by Scott Olson/Getty Images)

President Donald Trump for now has not met the requirements to send National Guard troops to Chicago, the U.S. Supreme Court ruled Tuesday afternoon in a major setback for the president.

The court’s majority rejected the Trump administration’s request to stay, or halt, a lower court’s order barring federalization of National Guard troops to assist federal immigration enforcement officers in Chicago. 

The president is only empowered to federalize National Guard units when the troops are enforcing laws that regular military forces are legally allowed to enforce, the court said in a ruling from its emergency docket that will apply while the merits of the case are argued.

The Posse Comitatus Act, passed in 1878, generally prevents the military from participating in civilian law enforcement.

The decision on the eve of a five-day holiday weekend for the federal government appeared to be 6-3, with three conservative justices, Samuel Alito, Clarence Thomas and Neil Gorsuch, dissenting. The ruling represented the first time the high court has weighed in on Trump’s use of the guard in several cities, though other legal fights continue.

The administration had not shown why the situation in Chicago, in which residents have protested aggressive immigration enforcement, should present an exception to the law, the court majority said.

“At this preliminary stage, the Government has failed to identify a source of authority that would allow the military to execute the laws in Illinois,” the majority opinion said.

In an emailed statement, White House spokeswoman Abigail Jackson said the ruling would not detract from Trump’s “core agenda.”

“The President promised the American people he would work tirelessly to enforce our immigration laws and protect federal personnel from violent rioters,” Jackson wrote. “He activated the National Guard to protect federal law enforcement officers, and to ensure rioters did not destroy federal buildings and property.”

Protecting federal officers

In a concurring opinion, Justice Brett Kavanaugh, whom Trump appointed during his first term, wrote that he agreed with the decision to deny the motion for a stay, but would have done so on narrower grounds.

The majority opinion was overly restrictive and would block the president from using National Guard forces to protect federal property and personnel, Kavanaugh said.

Alito wrote in a dissent, joined by Thomas, that their interpretation of the majority’s order could have far-reaching consequences that undermine the traditional role of the guard.

It would free National Guard members to enforce immigration law, but not to provide protection to the Immigration and Customs Enforcement officers who are assigned that function, Alito wrote. 

“Whatever one may think about the current administration’s enforcement of the immigration laws or the way ICE has conducted its operations, the protection of federal officers from potentially lethal attacks should not be thwarted,” Alito wrote. “I therefore respectfully dissent.”

Implications for other cities

The ruling is only in effect while the case, in which Illinois is challenging the administration’s deployment there, proceeds. 

But it marks a rebuke, including from a Trump appointee, of the administration’s strategy of deploying National Guard troops to assist in its aggressive immigration enforcement.

Trump has ordered troops to Los Angeles, Washington, D.C., Memphis, Tennessee, and Portland, Oregon, to either counter crime generally or assist federal immigration officials. Governors of Democratic-led states have strenuously pushed back against those deployments. Republican attorneys general have argued their states are harmed by the protests in Chicago and other cities that impede federal ICE officers from doing their jobs.

Illinois Gov. JB Pritzer in a statement praised the ruling. “Today is a big win for Illinois and American democracy,” he said. “I am glad the Supreme Court has ruled that Donald Trump did not have the authority to deploy the federalized guard in Illinois. This is an important step in curbing the Trump Administration’s consistent abuse of power and slowing Trump’s march toward authoritarianism.”