In arguments before the Supreme Court on Arizona’s SB 1070 immigration law last month, the elephant in the room—racial profiling and discrimination—made just a short-lived cameo appearance. When the Justice Department’s top lawyer rose to make the Obama administration’s case against SB 1070, the Chief Justice immediately demanded confirmation that “no part of your argument has to do with racial or ethnic profiling, does it?” A few moments later he reiterated: “OK. So this is not a case about ethnic profiling.”

The Chief Justice may have dismissed the idea, but racial and ethnic profiling is exactly what lies at the heart of the debate around SB 1070, a law that targets Arizona’s Latino population for continual stops, interrogations, and status checks. And while the Obama administration directly challenged Arizona’s controversial law on narrower grounds—that it violates federal law and hence is “preempted” under the Constitution—a discrimination claim could and should have been evoked as part of that legal principle. Indeed, years of judicial precedent, going back to the nineteenth century, demonstrates that ethnic discrimination against immigrants itself interferes with core principles of federal law.

To be sure, part of the reason why racial profiling is not directly before the Court is that the administration—importantly—challenged the law before it could go into effect, in order to stop its implementation. To do that, the Justice Department mounted a "facial challenge," which tries to stop the law when its broader impact, as measured by empirical evidence, is not yet available.

But the second and more troubling reason is the government's unduly narrow understanding of its own case. The legal claim of federal “preemption” compels courts to strike down state laws that interfere with federal primacy. But preemption is a famously malleable doctrine. Critical to the question of whether a state law is inconsistent with federal law is which laws the Court is asked to consider as part of the federal interest.

In the oral arguments, however, the Court considered only whether SB 1070 interferes with federal immigration law and federal immigration priorities. As a result, the justices' questions turned on whether Arizona’s mandate interfered with immigration enforcement, including the Obama Administration’s recent and laudable exercise of “prosecutorial discretion” that focuses deportation resources on those it deems as high priority targets.