Its aggressive law could spur action. Immigration has returned to center stage in the U.S. for wrong but not un-reasonable motives. The S.B. 1070 signed by Arizona Gov. Jan Brewer in April has set off an explosion of condemnations, justifications, and demonstrations. This brouhaha has brought the issue back to the fore, leading thousands to muse about, hope for, or decry the possibility of comprehensive reform. It is long overdue.The law essentially allows local authorities in Arizona to request documents at virtually any time from more or less innocent bystanders for pretty much any reason to prove their legal status in the U.S. While in theory the law is applicable to anyone, the fact that there are nearly 500,000 Mexicans in the state (many of them just passing through–it has been the preferred point of entry from Mexico for 15 years) means that it will be applied to "Mexican-looking" individuals. According to its defenders, this is not tantamount to racial pro-filing; in the view of its critics and potential victims, there is no other name for it. Brewer couldn’t explain what an illegal alien "looks like" when she signed the bill, but everyone knows what she and the law’s authors were thinking. The problem, of course, is that there are nearly 30 million American Latinos who "look Mexican," because their parents, grandparents, or ancestors were; there are 6 million Mexican legal permanent residents in the U.S., who, by definition, "look Mexican," and there are another 6 million unauthorized Mexicans in the U.S. who are the target of the Arizona law but have not violated any law, except for committing the Class B misdemeanor of entering the country illegally.In all likelihood the law will be struck down by the courts as unconstitutional. It will almost certainly never be enforced. But paradoxically, it does provide an opportunity for Barack Obama and Mexican President Felipe Calderón, who will meet in Washington on May 19-20, to join in pushing for a major overhaul of American immigration rules. For Obama, Arizona provides a chance to deliver on several promises and accomplish various objectives. He owes Latinos big time. Hispanics not only voted for him in overwhelming numbers, they turned out more than ever before. Now they can argue that comprehensive immigration reform is not only desirable but constitutes the only antidote to other states’ S.B. 1070s. Second, if, as Obama has said, contributing to Mexico’s well-being and strengthening the U.S.-Mexican relationship is paramount in his foreign policy, nothing could be more important to that than legalizing Mexicans already in the U.S., as well as those who will inevitably enter over the next decade. Yes, it is a divisive issue, and, no, the outcome is not certain. But this was also true for health care. More importantly, the Bush precedent is worth remembering: Obama’s predecessor truly wanted immigration reform. But he waited so long to push for it that when he did he was too weak to achieve it.As for Calderón, he decided from the outset of his mandate in 2006 to forsake immigration as a bilateral agenda item with the U.S. in favor of the war on drugs. He has never spoken out forcefully in favor of immigration reform in the U.S., nor has he raised his voice in the name of his 12 million compatriots in the U.S., other than to reiterate traditional Mexican bromides about human rights and the American economy’s demand for low-wage, low-skill labor. Now he has a chance to acknowledge that the fate of his countrymen stateside should be any Mexican president’s No. 1 foreign-policy priority. He can use his speech to a joint session of the U.S. Congress this month to make that case, and he should understand that the effectiveness of this stance is less important than its moral argument: the only spokesperson the 6 million Mexican migrants without papers have is their president, period.The two governments’ response to S.B. 1070 has been timely and right. Obama has criticized it explicitly and ordered the Justice Department to examine its constitutional validity. Calderón has issued a travel advisory to Mexicans regarding the perils of visiting Arizona, an especially relevant stance given that more than 30 percent of the state’s foreign trade is with Mexico. Now they must address the roots of the problem–the absence of U.S. federal action, and the obstacles to Mexican cooperation on the issue–as well as the long-term solution: filling the void that generated the border state’s nefarious behavior. Accepting this need and admitting that it requires joint action and responsibility would go against the grain, but in the direction of sense and sensibility. Thank you, Arizona.Castañeda is a former foreign minister of Mexico, Global Distinguished Professor at New York University, and a fellow at the New America Foundation.