The Obama administration's challenge to an Arizona immigration law will not hinge on the law's popularity or wisdom; state legislatures are permitted to enact unpopular and unwise laws. And as Chief Justice John Roberts observed — and the administration's lawyer agreed — this case is not about civil rights or racial profiling, either. The challenge to Senate Bill 1070 hinges on the narrow question of whether it conflicts with federal immigration law.

Since last week's arguments before the Supreme Court, supporters of the Arizona law are increasingly hopeful that the court will find it does not conflict with federal law and will uphold most if not all of it.

S.B. 1070 requires state and local law enforcement officials to verify the immigration status of those legally stopped if there is a "reasonable suspicion" that they are in the country illegally. It also allows arrests without a warrant if authorities have probable cause to believe a noncitizen has committed an offense that subjects him to deportation.

Those provisions are entirely consistent with federal law. Federal statutes allow state and local officials to communicate with federal officials to ascertain a person's immigration status. The federal government is also required to respond to state or local government inquiries about an individual's immigration status for any lawful purpose.

As the 10th Circuit U.S. Court of Appeals has noted, "Congress passed a series of provisions designed to encourage cooperation between the federal government and the states in the enforcement of federal immigration laws. … This collection of statutory provisions evinces a clear invitation from Congress for state and local agencies to participate in the process of enforcing federal immigration laws."

S.B. 1070 criminalizes the presence in Arizona of noncitizens without legal documentation. Federal law criminalizes any noncitizen's failure to register with the federal government and "at all times carry with him and have in his personal possession" proof of registration. There's no conflict with federal law there.

While federal law punishes employers who hire illegal immigrants, Arizona's statute makes it a crime for illegal immigrants to seek work. This is the provision most likely to be found in conflict with federal law, but it's debatable. Is it a conflict — or an example of a state accepting Congress' invitation "to participate in the process of enforcing federal immigration laws"?

At the root of the national debate over immigration is the unwillingness of Washington officials of both parties, including President Obama, to decide whether the United States should have open borders, with no limit on immigration, or should enforce the annual numerical limit on immigration enacted by Congress. It's a simple question: limits or no limits?

Federal officials don't want to repeal the limit and declare the borders open, which would be unpopular. But they also don't want to enforce the limit enacted by Congress, because that would require removing people who have entered the country in violation of the limit, which could cost them votes and support, too.

So we end up with the current illogical policy of maintaining a legal limit but refusing to enforce it against anyone who hasn't been convicted of a serious crime and isn't a national-security threat. This incoherent policy leaves Arizona, which shares 370 miles of border with Mexico, in the lurch.

Illegal immigrants are believed to account for 400,000 of Arizona's 6.4 million residents, which has caused a continuing crisis over the cost of public education, emergency health care, law enforcement, and incarceration. In 2005, then-Arizona Gov. Janet Napolitano, who is now Obama's homeland security secretary, declared an immigration emergency in the state, saying, "The federal government has failed to secure our border, and the health and safety of all Arizonans is threatened daily. ..."

Whether you think S.B. 1070 is good policy or not, everyone should understand why the Arizona Legislature enacted it — and why the Supreme Court is likely to uphold it.

Jan C. Ting is a professor of law at Temple University Beasley School of Law. He can be reached at