“ARIZONA AND its 370-mile border are a conduit for rampant illegal entries and cross-border smuggling to a degree unparalleled in any other State.” So argue lawyers for Arizona in a case the Supreme Court is scheduled to hear Wednesday. Although immigration has in fact declined, the state says that the “public safety and economic strains” created by a porous border “have created an emergency situation, which demanded a response.”

The response was Arizona’s S.B. 1070, a 2010 immigration bill that empowers state and local law enforcement officers to detain those suspected of being in the country illegally. It also provides for criminal charges against illegal immigrants who seek or secure employment in the state.

The Obama administration pushed back hard and early, arguing even before the law was implemented that it unconstitutionally trod on the federal government’s exclusive rights to enforce immigration laws and conduct foreign policy. A federal trial judge and the U.S. Court of Appeals for the 9th Circuit blocked implementation of the provisions. Now the Supreme Court will hear arguments on whether the Arizona provisions are forbidden, or “pre-empted,” because they incur on legal territory that is the exclusive domain of the federal government. Although Arizona has been widely — and we believe, rightly — criticized for a law that threatens the constitutional rights of legal and illegal immigrants alike, such questions are not at play in this case.

The state went too far when it essentially overrode Congress, which had decided to penalize those who hire unauthorized workers, rather than the workers themselves. Workers are governed by different aspects of federal immigration law and can face penalties for providing false documentation to assert their legal status. Congress, in other words, spoke directly to this issue, and Arizona’s law is a direct affront to that considered judgment.

The provisions pertaining to local and state law enforcement’s power to verify a suspect’s immigration status or to detain those suspected of being in the country illegally represent a closer call. The federal government — through such programs as “Secure Communities” — often requires local officials to verify the immigration status of those arrested on state or local charges. Arizona’s law goes further, directing officers to check the status of those who they believe “have committed any public offense that makes the person removable from the United States.” This arbitrary and unnecessarily invasive measure would surely offend the Constitution’s Fourth Amendment if this question were before the court. But does federal law clearly prohibit what Arizona says is its effort to be an aggressive partner in ensuring that federal immigration standards are enforced — especially when the federal government retains exclusive authority over removal or deportation? Not so clear.

What is certain is that immigration policy would be even more dysfunctional if states were given the green light to craft and enforce their own laws. This legislative hodgepodge would sow confusion, invite abuse and encroach on the president’s constitutional prerogative to be the authoritative voice of the country on foreign affairs. Of course, the best way to keep states out would be for Congress and the White House to pass legislation that explicitly rejects state interference on the immigration front while addressing legitimate security concerns and paving a path to citizenship for undocumented immigrants.