June 26 (Bloomberg) -- The Supreme Court handed down a mixed ruling on Arizona's immigration law, upholding by a 5-to-3 majority the lower court's decision barring enforcement of three provisions of the law, but unanimously reversing the Ninth Circuit's decision halting enforcement of the law's most controversial provision.

     That section directs Arizona law-enforcement officers to investigate a person's immigration status whenever, during a lawful stop, they have reasonable suspicion that the individual is in the U.S. unlawfully. The provision, Section 2B, specifically prevents a person's race or ethnic background from being considered to determine this reasonable suspicion.

     As Justice Samuel Alito noted in his concurring opinion, "The United States' argument that 2B is pre-empted, not by any federal statute or regulation, but simply by the Executive's current enforcement policy is an astounding assertion of federal executive power that the Court rightly rejects."

     To be sure, the majority opinion, written by Justice Anthony Kennedy, raised some red flags indicating that Section 2B might be enforced in unconstitutional ways and therefore lead to new constitutional challenges. But the opinion serves as a roadmap, both for Arizona and for other states waiting in the wings with immigration-enforcement statutes of their own. It will enable them to exercise their police powers in ways that help protect the lives and property of lawful residents against an onslaught of illegal immigration and deliberate under-enforcement of existing laws by the federal government. That is very good news for the states.

Not Devastating

     Less good, but not devastating, is the court's decision on three other sections of the Arizona law, known as SB 1070. States can't impose parallel criminal sanctions for failure to carry the immigration papers required by federal law. They can't impose criminal sanctions on employees who seek work that is illegal for them to seek. And they can't make warrantless arrests based on a probable cause that a person has committed an offense subjecting him or her to removal under federal immigration law.

     These tools would have bolstered the states' efforts and should have been upheld, based on a proper understanding of state sovereignty and federal pre-emption doctrine. Nevertheless, Arizona's success in defending Section 2B and its success in the lower courts in defending all the other provisions of the law leave it with ample authority to get a handle on the collateral consequences of illegal immigration into the state. It is a state crime, for example, to stop to hire day laborers (many of whom will be illegal immigrants), if doing so impedes traffic. It is a state crime to knowingly employ illegal immigrants. It is a state crime to transport or harbor illegal immigrants. Law enforcement can impound cars used in the transportation of illegal immigrants.

     Most significantly, Arizona citizens have a cause of action against any state or local official who fails to cooperate in the enforcement of federal immigration law. The lower courts didn't hold the "anti-sanctuary city" provisions of SB 1070 to be unconstitutional, and those provisions remain on the books and enforceable, unaffected by the Supreme Court's ruling.

     So where do I think Justice Kennedy's majority opinion went astray? In striking down the three provisions of the Arizona law that it did, it bucked a recent trend of the court with respect to its pre-emption doctrine. There is no question that, in exercising its powers over naturalization and immigration, Congress can expressly pre-empt various state laws that would conflict with the federal law. But there was no express pre-emption provision in federal law that prohibited Arizona's efforts.

Kennedy's Pre-Emptions

     Justice Kennedy thus had to resort to various implied pre-emption doctrines, about which the court has grown increasingly suspicious. Field pre-emption, for example, has in the past recognized that when Congress so comprehensively occupies an entire field of the law, we can infer that it intended to displace any state authority over the subject. And "policy" pre-emption yields the view that states can't act if, in the court's judgment, they are undermining unspoken policy goals of the congressional statutory plan.

     Both doctrines require the justices to engage in the highly speculative enterprise of what Congress might have intended by its silence, and, as I said, the court has grown increasingly suspicious of the very legitimacy of that enterprise.

     Not so with Justice Kennedy's opinion, which embraces both doctrines. Congress's decision not to impose federal criminal sanctions was viewed as a deliberate decision to bar states from imposing state criminal sanctions. But, as the dissenting justices pointed out, it is an equally plausible inference that Congress simply wished to leave the matter of whether to impose state criminal sanctions to the states.

     Normally, any such ambiguity would be interpreted to the benefit of the states, because in other areas of the law, the Supreme Court has been pretty adamant that the displacement of state sovereign authority can only be done with the clear and unambiguous determination of Congress. In other words, there is normally a presumption against pre-emption.

     That presumption will no longer apply as vigorously in the immigration context in areas where the federal government has extensively regulated. That is unfortunate, but not debilitating, because the states retain a good number of tools that they can use to deal with the consequences of illegal immigration within their borders.