President Donald Trump’s deployment of nearly 4,000 National Guard troops and 700 U.S. Marines to Los Angeles has exceeded the legal limits of how the military can be used to enforce domestic laws in American cities.

The Governor of California, Gavin Newsom, intends to prove that in a court of law. The state has filed a lawsuit alleging, “President Trump has repeatedly invoked emergency powers to exceed the bounds of lawful executive authority.”

“On Saturday, June 7, he used a protest that local authorities had under control to make another unprecedented power grab, this time at the cost of the sovereignty of the state of California and in disregard of the authority and role of the Governor as commander-in-chief of the state’s National Guard,” says the complaint, which was filed in federal court.

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U.S. District Judge Charles R. Breyer agreed. Breyer, a Bill Clinton appointee who also happens to be the brother of retired Supreme Court Justice Stephen Breyer, declared that Trump’s “actions were illegal — both exceeding the scope of his statutory authority and violating the Tenth Amendment to the United States Constitution,” and ordered control of the National Guard returned to Newsom. The order was supposed to take effect Friday at noon, but the 9th U.S. Circuit Court granted an administrative stay late Thursday night, pausing — at least temporarily — Breyer’s order.

What this lawsuit comes down to is the Insurrection Act versus the Posse Comitatus Act. One act is more than 200 years old and the other, nearly a century and a half.

The Insurrection Act, passed in 1807, authorizes the president to deploy military forces inside the United States to suppress rebellion, invasion or to enforce federal law in certain situations. The Posse Comitatus Act, passed in 1878, was put in place to ensure that the federal military would not be used to intervene in the establishment of Jim Crow laws in the former Confederacy after Reconstruction. The overarching principle of the Act is to prevent the military from interfering in the affairs of civilian government.

When it comes to the Insurrection Act, troops can be deployed under several sections of the law. The statute’s requirements are not clearly defined, leaving some aspects of the law to the discretion of the president. One provision provides that the president can send in troops at a governor’s request. A second provision provides the president with the authority to deploy troops to “enforce the laws” of the United States or to “suppress rebellion” whenever unlawful obstructions make it difficult to enforce federal law — even against the state’s wishes.

A third provision provides if anyone in a state is being deprived of a constitutional right and state authorities are unable or unwilling to protect that right — think Presidents Dwight D. Eisenhower and John F. Kennedy following Brown v. Board of Education — the president can deploy troops.

“He [Trump] is declaring utterly bogus emergencies for the sake of trying to expand his power, undermine the Constitution and destroy civil liberties,” Ilya Somin, a libertarian professor at Antonin Scalia Law School, told the New York Times.

Now let’s juxtapose the Insurrection Act with the Posse Comitatus Act. The Posse Comitatus Act consists of just one sentence: “Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.”