The state of Arizona has argued that its controversial immigration law merely supplements federal efforts to address illegal immigration. The governor and other state officials have insisted that if the federal government will not enforce adequately federal law, then a state should have authority to get the job done. On Monday, the U.S. Supreme Court rightly reaffirmed that the federal government has broad power to set immigration policy. The country hardly benefits when states follow their own course, inviting inconsistency, confusion, ineffectiveness, or worse.

Make no mistake, Arizona has not sought simply to be more assertive within the bounds of federal law. A 5-3 court majority struck down three of four provisions that go too far, the state seeking to trump federal power. Writing for the majority, Justice Anthony Kennedy noted Arizona’s “understandable frustrations” with illegal immigration, yet he added that “the state may not pursue policies that undermine federal law.”

Undermine? Congress already has made it illegal to be in the country without proper authorization. The Arizona law makes it a state crime, with fines and possible imprisonment. What the high court reminded is that Congress, in enacting immigration rules and policies, did not carve into the law such a complementary role for the states.

The Arizona law makes it a state crime for illegal immigrants to work or to try to find work. Yet Congress has chosen not to make working illegally in this country a criminal offense. Federal law penalizes employers who hire illegal immigrants. Illegal immigrants working here may face civil infractions. The court stressed that states cannot add criminal penalties that Congress did not establish.

Arizona calls for police officers to make arrests — without warrants — if they have probable cause to believe a deportable offense has been committed. The court explained that only the federal government has the authority to determine when or whether someone should be arrested for being illegally in this country.

The court majority did not strike down the troubling “papers, please” provision of the Arizona law. The provision requires police officers to check the immigration status of anyone they stop or arrest — if there is reason to believe the person might be an illegal immigrant. The court made plain its uncertainty about whether the provision is valid or not. It will wait for the practical application, emphasizing what it will not tolerate: any appearance of racial profiling.

For Arizona and other states, including Indiana, that have enacted similar laws, the court’s message is firm: The federal government has the task of shaping immigration policy, as it should, given the risk of incoherence if states are permitted to take their own paths. Immigration is national in scope, requiring the federal government in charge.

What those in Washington should not miss is the worthy aspect of the Arizona law, the local frustration reflecting the need for a comprehensive update of the approach to immigration. Regrettably, that seems a far reach in view of the partisan divide, too many unwilling to strike the necessary balance. To its credit, the Supreme Court has reinforced where the authority resides.