Arizona might be going to the U.S. Supreme Court yet again. A federal appeals court upheld part of the Grand Canyon State’s voter-ID law but struck down another part of Arizona’s law as inconsistent with a 1993 federal law. This might become the third citizen/voting Arizona law to go to the Supreme Court in just three years.

Arizona allows for citizens to adopt ballot propositions with the force of law, which trump state statutes but fall short of amending the Arizona Constitution. Arizona’s voters adopted Proposition 200 in 2004. It requires showing proof of citizenship when you register to vote, and then showing government-issued photo-ID on Election Day when you cast your ballot.

Several individuals and groups sued, arguing that these requirements violate two provisions of the U.S. Constitution and also the National Voter Registration Act of 1993 (NVRA), which had been passed by a Democrat-controlled Congress and signed by Bill Clinton. After years of litigation, the case was decided by the U.S. Court of Appeals for the Ninth Circuit.

Although federal appeals are heard by three-judge panels, on rare occasions the full appeals court will reconsider a panel decision in what is called an en banc rehearing. The Ninth Circuit is so large (almost thirty active-service judges) that when it does an en banc rehearing, the court’s chief judge hears it, along with ten other judges chosen at random. They took this unusual step in this case, Gonzalez v. Arizona.

Judge Sandra Ikuta—appointed by George W. Bush—wrote the majority opinion. In 2008, the Supreme Court upheld Indiana’s voter-ID law in Crawford v. Marion County Election Board in a 6−3 decision. Arizona’s law is similar to Indiana’s, so the Court upheld it easily, holding that Arizona’s law is consistent with the U.S. Constitution.

Not so the provision requiring people show proof of citizenship when registering. The traditional way to register is by filling out a state form at your county courthouse or county building. NVRA created two new ways a person can register to vote in federal elections. One is by filling out the state form at your local Department of Motor Vehicles office, and the other is by filling out a federal form at home and submitting it by mail. The plaintiffs in the Gonzalez case used the federal form—which makes you declare that you are an American citizen but does not ask for proof—and says that Arizona’s law violates NVRA.

The general rule is that when federal and state laws conflict, federal law wins. This almost always happens under the Supremacy Clause of the Constitution. But election law issues arise under the Elections Clause of the Constitution, which says that states have primary responsibility for conducting elections but that “Congress may at any time by Law make or alter such [state] Regulations.”

The Supreme Court has previously held that the Elections Clause sets a higher bar for states than the Supremacy Clause. To respect state sovereignty, courts presume a state law is not preempted by federal law under the Supremacy Clause unless Congress makes explicitly clear that it wants to trump the states. If that were the rule in Gonzalez, then Arizona’s law would win on both issues in this case.

But the Supreme Court has not to date applied that same rule to election laws. Instead, it has said that federal election law automatically displaces state election laws. So even though there is a way to make Arizona’s statute coexist alongside NVRA, the Ninth Circuit held that Arizona’s citizenship-proof requirement must go.

Chief Judge Alex Kozinski joined the majority but also wrote a separate concurring opinion. In it, Kozinksi observed that, “the Supreme Court has never articulated any doctrine of giving deference to the states under the Elections Clause… A case such as ours, where the statutory language is unclear and the state has a compelling interest in avoiding fraudulent voting by large numbers of unqualified electors, presents a far more suitable case for deciding whether we should defer to state interests. But only the Supreme Court can adopt such a doctrine.”

So the messy split here, with some judges voting to strike down one provision, others voting to uphold both, and others voting to strike down both, might make this a tempting case for the Supreme Court to take. The fact that Kozinski—a libertarian appointed by Ronald Reagan and one of the most brilliant judges on the entire federal bench—wrote that only the Supreme Court can reorient the Elections Clause, and that it should do so here, increases the odds that the justices will take the case.

In the end, this was an important win for voter-ID laws. And if the justices take this case, it could become a broad-based win that would strengthen state sovereignty and diminish centralized federal control of the democratic process on Election Day. That would be a welcome development.

Ken Blackwell is former Ohio Secretary of State and U.S. Ambassador to the United Nations Human Rights Commission. Breitbart legal contributor Ken Klukowski is a fellow with the American Civil Rights Union and on faculty at Liberty University School of Law.