Given the frosty reception the Obama Administration received from the U.S. Supreme Court during April’s oral arguments, today’s decision in the Arizona immigration case was probably the best that the Administration could have hoped for. The decision upholding the key provision of the Arizona’s immigration law can nonetheless only be viewed as a significant defeat for the Administration.

In filing suit in 2010 against the Arizona law (SB 1070), the Administration essentially took the position that States are permitted to assist with immigration law enforcement only to the extent that the Executive Branch explicitly calls for assistance. Thus, in challenging § 2(B) of SB 1070 – which directs Arizona law enforcement officers to check the immigration status of anyone they have lawfully stopped, whenever they have a reasonable suspicion that the individual is an illegal alien – the Administration argued that § 2(B) skews enforcement priorities by forcing federal officials to respond to what it anticipated would be a groundswell of requests for immigration-status information. The Court found no merit in that argument, noting that a federal statute explicitly encourages States to assist with immigration enforcement by asking for information on immigration status of those in its custody.

In other words, although all agree that federal authorities have the final say regarding which aliens are permitted to remain in the country, the Court could not have been clearer that States have an important role to play in immigration law enforcement. Arizona has every right to attempt to determine who among those in its custody are in the country illegally, and then offer to turn over to the federal government those determined to be illegal. As the Court recognized, § 2(B) provides that Arizona officials will do no more than that; any decision regarding whether to deport the illegal aliens or release them will be up to the federal government.

Ironically, the only argument against § 2(B) that the Court deemed potentially viable was not even raised by the Solicitor General; instead, the argument was raised by a supporting amicus curiae. The Court said that § 2(B) “would raise constitutional concerns” if, once it begins to be enforced, it unnecessarily delays the release of some detainees “for no reason other than to verify their immigration status.” It would be surprising if opponents of § 2(B) could ever prevail on that argument on remand, however; armed with the guidance provided by today’s decision, Arizona almost surely will instruct law enforcement personnel to avoid such delays. If the federal government cooperates with Arizona and provides timely responses to requests for immigration status, the potential for such delays will be virtually non-existent. If, on the other hand, the federal government balks at providing timely information, Arizona presumably will direct law enforcement personnel to release the detainees in question temporarily, until the immigration status check is completed. Of course, if those released turn out to be illegal aliens and cannot be re-detained because they cannot be located, federal officials responsible for the delays may have a difficult time explaining themselves.

The Court ended up striking down three other less-important provisions of SB 1070. The Court acted on narrow grounds; it deemed the three provisions to be in conflict with specific immigration laws adopted by Congress. If Congress disagrees with that assessment, it is free, of course, to amend the federal laws in question to make clear that it did not intend to preempt the three Arizona provision. More importantly, nothing that the Court said in striking down those three provisions undercuts the overriding message of today’s decision: the enforcement of immigration laws is not the exclusive domain of the federal government. Rather, States have an important role to play in enforcing immigration law, and those States that follow the guidelines established by the Court’s decision need not fear judicial interference with their enforcement efforts.