President Obama had it about right, in my view, when he called Arizona’s new immigration law "misguided" and a threat to "basic notions of fairness" and to "trust between police and our communities."

Similar misgivings — filtered through a legal doctrine called "field pre-emption" — seem more likely than not to persuade the courts to strike the law down.

But please, let’s can the hysteria. The problems with this law — and with copycat proposals in at least 10 other states — are a far cry from the images of Nazi Germany, apartheid, and the Jim Crow South conjured up by leftists who would denounce any effort to discourage illegal immigration.

To correct some misconceptions:

• The solid majority support for the law among Arizonans — and the 51 percent support among other Americans who told Gallup pollsters that they had heard of the Arizona law — is not driven by racism. It’s driven by frustration with the federal government’s failure to protect Arizona and other border states from seeing their neighborhoods, schools, hospitals, and prisons flooded by illegal immigrants. Worse, "It’s terrifying to live next door to homes filled with human traffickers, drug smugglers, AK-47s, pit bulls, and desperate laborers stuffed 30 to a room, shoes removed to hinder escape," as Eve Conant reported in Newsweek.

• Although it’s true, and most unfortunate, that absent robust administrative safeguards the Arizona law could lead to racial profiling by police, it certainly does not require racial profiling. Indeed, a package of revisions signed on April 30 by Arizona Gov. Jan Brewer seeks to prohibit racial profiling. The revisions did this by deleting the word "solely" from the original, April 23, law’s provision barring investigation of "complaints that are based solely on race, color, or national origin."

• Nor does the new law, as revised, empower police officers to stop anyone they choose and demand to see their papers. Rather, it authorizes such demands only after "any lawful stop, detention, or arrest made by a law enforcement official," and only if "reasonable suspicion exists" — apart from ethnicity — that the person "is an alien and is unlawfully present in the United States." Some of the law’s language could tempt police to demand papers from people suspected of petty violations of civil ordinances such as having an overgrown lawn, but it’s unclear how that will play out in practice.

• Neither is it fair to say — as did a New York Times editorial — that Arizona’s "defining the act of [an alien’s] standing on its soil without papers as a criminal act is repellant." In fact, since 1952, the law of the United States has defined the act of an alien’s standing on its soil without papers as a criminal act.

So is there a problem with Arizona stepping in to enforce its own identical copy of a federal law that the feds barely attempt to enforce?

The problems with this law are a far cry from the images of Nazi Germany, apartheid, and the Jim Crow South conjured up by leftists who would denounce any effort to discourage illegal immigration.

Actually, there is a problem. It’s more subtle than suggested by the dependably hyperbolic Times editorial page. But it may well persuade the courts to find the new Arizona law unconstitutional.

The Supreme Court has long held that by adopting a comprehensive regulatory regime for immigration matters, Congress has manifested an intent to "pre-empt the field" and thus to sweep away state laws addressing the same issues.

To be sure, federal immigration laws do not specify that states may not do what Arizona has done. Nor do they conflict directly with the Arizona law. So the pre-emption challenges now being prepared by civil-rights groups and others are not sure to succeed.

But they aren’t sure to lose, either. The Supreme Court has held that federal law regulates immigration so comprehensively as to pre-empt any state law — even one purporting to help enforce federal law — that "stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress." So said the justices, in Hines v. Davidowitz, in 1941.

The strongest argument for federal pre-emption of the Arizona law is that Congress has carefully balanced the need to pursue the most-dangerous criminals among the estimated 12 million to 20 million illegal immigrants in the U.S. against the risk of harm from overly aggressive or arbitrary pursuit of hard-working people who immigrated — legally or illegally — years ago.

The justices may well hold that "Congress would prefer to have U.S. agents making the decisions about what individuals are realistic suspects," says a leading Supreme Court litigator who declined to speak for attribution, "and not having potential vigilante groups (even if they are wearing a badge) running around sweeping up individuals, many of whom are here legally."

Another consideration is the pre-eminence of the federal government in matters touching on foreign affairs. Mexican President Felipe Calderon, among others, has sharply condemned Arizona’s action.

Although a 1976 decision, De Canas v. Bica, recognized an exception to the pre-emption doctrine for state laws regulating conduct of only "peripheral concern" to the federal immigration laws, the issues raised by the new Arizona law seem more than peripheral.

All of this may sound rather technical and abstract, and you may wonder: Is that really the way that judges and justices think? Don’t they worry about how the Arizona law will affect the lives of real people?

Of course they do. But that begs the question of which real people have the best claim on what Obama used to call judicial "empathy." The hard-working Mexicans and Central Americans whose crime (a misdemeanor, under both federal and Arizona law) was sneaking across the border long ago to seek a piece of the American dream? The legal immigrants and children of immigrants who fear being hassled by racial-profiling police? The other Arizonans who feel that they are being overrun by illegal immigrants and fear that the murderous Mexican drug lords’ reign of terror is starting to spread across the border?

Principled judges and justices are less comfortable making such open-ended value judgments — or, to be precise, making them overtly — than they are following precedents that weigh such apparent abstractions as whether an admittedly failed federal regulatory regime should pre-empt a chaotic collection of inconsistent state laws that might, or might not, deepen the dysfunction.

The bottom line is that it’s a pretty good bet that the four more-liberal justices, including any successor to retiring Justice John Paul Stevens, would vote to strike down the Arizona law. And even if all of the four more-conservative justices went the other way — no sure bet — swing-voting Justice Anthony Kennedy might well vote with the liberals.

A Supreme Court decision striking down the Arizona law would be most likely if there were evidence by the time the case reached the justices of police abuses so serious and widespread that the only effective remedy would be wholesale invalidation.

And therein lies a paradox: If civil-rights groups and other plaintiffs succeed in persuading lower federal courts to block the law from taking effect — and thus from spawning any police abuses — they may well hurt their own chances of prevailing in the Supreme Court.

So they might be wise to wait for evidence of real police abuses rather than rushing to sue over potential abuses — which seem somewhat less likely after the April 30 revisions than before. But the race to raise funds by piling lawsuits atop hyperbolic rhetoric is on.

The Obama administration faces a similar quandary, and others, in deciding whether to file its own court challenge.

Homeland Security Secretary Janet Napolitano testified on April 27 that the Arizona law will "detract from and siphon [federal] resources that we need to concentrate on those… who have committed the most serious crimes." But she could avoid that outcome — while taking some political heat — simply by instructing federal agents not to cooperate with Arizona police in enforcing the new law.

Meanwhile, an extraordinarily broad coalition of immigrant, civil-liberties, business, and other groups — including virtually all of those attacking the new Arizona law — has urged the Supreme Court to review and strike down another Arizona immigration law, which was adopted in 2007 to punish employers of illegal immigrants.

The justices asked Solicitor General Elena Kagan more than six months ago to take a position on the plaintiffs’ petition. She has not yet responded.

Might the delay have something to do with the fact that it was Napolitano, then governor of Arizona, who signed the 2007 law? Or the fact that Kagan, a leading contender to fill Stevens’s seat, will be savaged by many conservatives if she attacks either Arizona law and by many liberals if she defends either of them?

Inquiring minds in Congress will want to know.

This article appeared in the Saturday, May 8, 2010 edition of National Journal.