In a historic though tentative ruling, a deeply divided Supreme Court ruled Tuesday that President Trump may not call up and use National Guard Troops to keep order in America’s cities.

Some parts of the ruling were supported by only five Justices, but that is a clear majority.  If it holds, after the controversy is confronted again in the future, it would mean that a 147-year-old law may withhold the authority that Trump used in sending National Guard troops to stop violence in Chicago and its near suburban areas.

Two of the Court’s large conservative bloc, Chief Justice John G. Roberts, Jr., and Justice Amy Coney Barrett, joined the three liberal Justices in the broadest part of a three-page ruling. The liberals were Justices Ketanji Brown Jackson, Elena Kagan and Sonia Sotomayor.  The lead opinion was unsigned, but clearly spoke for the majority.

A sixth conservative Justice, Brett M. Kavanaugh, joined only the narrowest part of the majority opinion, and wrote a separate four-page opinion arguing that the majority had gone too far to restrict presidential power to protect officers of the government in protecting themselves and federal property when violence erupts in U.S. cities, as it often has during President Trump’s sweeping nationwide campaign to arrest and deport foreign nationals who do not have a legal right to be in the U.S.

Although Justice Kavanaugh appeared to be open to more presidential power than the majority seemed to allow, he did stress in an important footnote that immigration enforcement agents need some proof of illegality among foreign nationals before arresting them and may not take individuals into custody based on their race.

While the restrictions tentatively imposed by Tuesday’s majority were significant, they did leave open the possibility that President Trump may invoke other federal laws to justify rigorous enforcement of immigration laws, and might even have unspecified power simply because he is the nation’s Commander in Chief with very broad powers.

It is not clear when this controversy will move to the next stage before the

Supreme Court.  Tuesday evening’s action was limited to the temporary question of whether the Court would allow Trump to send National Guard troops to Illinois when riots broke out over immigration enforcement actions.

The majority result was based on the majority’s tentative interpretation of an 1868 federal law, barring the use of Guard troops to engage in homefront policing duties, the so-called “Posse Comitatus Act,” and its reading of a 1908 lsw that allows the President to call up the National Guard if the U.S. military cannot handle a homefront uprising or a military invasion.

If the majority’s views as expressed this time are repeated in a more formal way in the future, they would put significant restraints on how President Trump and future Presidents make use of the National Guard – troops that normally are a part of state government, not the federal government.

The Court’s two most conservative Justices, Samuel A. Alito, Jr., and Clarence Thomas, joined in a robust 16-page dissenting opinion written by Alito.  It accused the majority of raising issues beyond those that were actually at stake, and of going far to compromise the President’s ability to deal with violence inside America.

Justice Neil M. Gorsuch, who is often a strong conservative voice, confined his writing to a two-page dissent contending that the Court should not have reached out at this stage to decide a host of “weighty questions” that potentially are at stake.  He gave no reliable indication of how he personally would vote on those questions if they were properly before the Court.

An important facet of this controversy was that the Justices, in finding a way to decide at least tentatively the dispute over the National Guard, was reacting to a legal brief filed by a Georgetown University law professor, Martin S.. Lederman, on the history of the use of the military during domestic uprisings.  The majority’s key points about the scope of the 1868 and 1908 laws closely tracked the professor’s arguments.  That is not rare, but it is not common.