Editor's note: Jeffrey Toobin is a CNN senior legal analyst and a staff writer at The New Yorker. A former assistant U.S. attorney, Toobin is the author of several critically acclaimed best-sellers, including "The Nine: Inside the Secret World of the Supreme Court" and "Too Close to Call: The 36-Day Battle to Decide the 2000 Election."
New York (CNN) -- The Arizona immigration law goes into effect on Thursday -- maybe. On July 29, it will be 90 days since the end of the legislative session -- which is the time when Arizona laws go on the books -- but the controversial measure has already drawn the first of many court challenges.
The question, then, is whether a judge will stymie the will of Arizona's legislators and governor.
There is no simple or obvious answer, in part because the law has many separate provisions and some are more controversial than others. And while the Obama administration and several civil rights groups are both challenging the law, they have very different rationales for why the law should be struck down. Sorting out all the possibilities may take some time.
For starters, then, what does the law, known as SB 1070, really provide?
The most controversial part of the law requires local police, who have made a "lawful stop, detention or arrest" of an individual, to determine that person's immigration status if there is "reasonable suspicion" that the person is an illegal alien.
What does this provision mean? Critics of the law have argued that it calls for racial profiling of Hispanics -- that it will lead police to stop and demand papers from law-abiding citizens or aliens who are doing nothing more than minding their own business. The law, according to these critics, violates the 14th Amendment right to equal protection of the laws. But while the profiling claim has generated the most publicity, the legal challenge to this part of the law rests on an entirely separate basis.
The Constitution and federal law says that immigration -- like all matters relating to foreign policy -- is a responsibility of the U.S. government, not the states. The Supremacy Clause of the Constitution also provides that when federal and state law conflict, it is the U.S. law that will always carry the day.
It is these provisions that underlie the Obama administration's challenge to the Arizona law. The Justice Department argued that SB 1070 undercuts the federal government's right to control immigration and the nation's borders.
In defending the law, Arizona claims that the state is entitled to work cooperatively with the federal government on immigration matters, especially when the U.S. government has failed to police its borders. At a hearing in federal court in Phoenix two weeks ago, Judge Susan Bolton seemed receptive to that argument.
"Why can't Arizona be as inhospitable as they wish to people who have entered or remain in the U.S. unlawfully?" she said.
"It's not for one of our states to be inhospitable the way Arizona has," said Edwin Kneedler, the Justice Department lawyer. "It is a direct intrusion into immigration matters and immigration enforcement. It interferes with the enforcement discretion of the federal agencies charged with enforcing those provisions and immigration laws generally."
Another Arizona lawyer responded, "The plaintiff over here is telling us we can't really do anything about the illegal immigration problem. 'Live with the status quo.' That's our national policy. The status quo is simply unacceptable."
According to those present in the courtroom for the hearing, Bolton looked to be trying to break the problem down into pieces, rather than give a thumbs-up or thumbs-down on the law as a whole.
The judge seemed especially concerned about the provision of the law that said local police in Arizona were required to check the immigration status of all arrestees.
"If this was extended throughout the nation, if every state adopted something like this, there would be a huge surge in requests" to the Department of Homeland Security's Immigration and Customs Enforcement division, Kneedler said. The judge suggested that Arizona does not have the right to impose these kinds of new burdens on the federal government.
On the other hand, Bolton seemed less impressed by the arguments of the civil rights groups who asserted that the law discriminated against Hispanics. She appeared to agree with lawyers for Arizona who said that any predictions of discrimination were speculative and that the law should be allowed to go into effect.
Besides, an Arizona lawyer asserted, there are simply too many Hispanics in Arizona for the police to turn against all of them. "If we were in Iowa, I could maybe understand. In Arizona we have a tremendous Hispanic heritage," John Bouma said. "All this hypothetical that we're going to go out and arrest everyone who looks Hispanic. Look around, it's impossible."
In any event, it's unclear whether the judge will rule before the law takes effect, or whether she will wait to see how it plays out in practice. And the losing party will almost certainly appeal, first to the Circuit Court of Appeals and then, ultimately, to the Supreme Court.
Immigration is not going away as a political issue and, thanks to this case, the legal issue is not going away any time soon either.
The opinions expressed in this commentary are solely those of Jeffrey Toobin.