In 1993, Congress passed what is known to most people as the Motor Voter Law, which required states to provide for voter registration as part of the driver’s license process. Of equal importance is another provision that created a federal form that states would have to “accept and use” to register their voters for federal elections, although they are also permitted to use their own forms as an alterative.

Congress wanted to be sure that the form had the basic information needed, but that it not be made too complicated and burdened with unnecessary requests for information. The statute set forth what can be required and allowed the Federal Election Commission (and since 2002, the Election Assistance Commission) to approve state requests to supplement the form.

The form currently requires the applicant to confirm that he or she is a U.S. citizen, but that was not enough for Arizona. It wanted to require all applicants to submit proof of citizenship with the form so that Arizona could assure that its admittedly valid law permitting only citizens to vote was being followed. But the U.S. Supreme Court, by a vote of 7-2, in Arizona v. Intertribal Council of Arizona, with Justice Antonin Scalia writing, and justices Clarence Thomas and Samuel Alito Jr. in dissent, said no: The best reading of the “accept and use” clause was that states could not require additions to the federal form unless the Election Assistance Commission went along with a state’s request, which it had not done here because it divided, 2-2. Among the reasons that support that outcome are the text of the law; the fact that Congress gave states a way to supplement the federal form for use in their state; and the reality that states could render the federal form irrelevant if they could impose additional requirements like proof of citizenship.

The practical considerations are significant because of one important way that the federal form has been used to increase registration. Citizen groups of all stripes go to places where young (and sometimes not so young) voters congregate — like rock concerts — and use the federal form to register voters from any state, without having to worry about unapproved state requirements, especially those that would require the applicant to attach copies of what Arizona considers adequate proof of citizenship. After all, how many people carry around their passports or birth certificates? And while most of us have our driver’s licenses with us, unless the voter registration group brought with them a portable photocopier that does not have to be plugged in, there will be no way to attach the copy needed to satisfy Arizona.

The victory may be short-lived, however, or at least significantly undercut, if Arizona is serious about wanting to have every voter prove that he or she is a U.S. citizen. The current laws, both Arizona and federal, apply only to the registration process, but Arizona could change its law to forbid anyone from voting without having first established his or her U.S. citizenship. Arizona might say, “You can do it when you register, or you can do it before Election Day, or on Election Day, but you have to do it once at some time.” If a voter had an Arizona driver’s license, that would be enough because the state now requires proof of citizenship for to obtain one. But for recent arrivals, and for those who do not (or do not any longer) drive a car, they may have to bring their passport (if they have one) or their Social Security card (if they can find it).

If this case had been decided a few years ago, there is not much doubt that Arizona would have amended its law to provide for proof of citizenship before voting. But having been slapped down several times in recent years by the Supreme Court, and perhaps with a heightened sense of wanting to avoid being on national television with huge delays while its election officials cross-examine senior citizens who took the bus to the polling place because they wisely gave up their cars, Arizona may think twice. As opponents already pointed out, it is a crime to lie about your citizenship or vote when you are not eligible, and for most people those constitute sufficient deterrence, especially when the maximum gain from the illegal acts would be one additional vote for the candidates of your choice.

Suppose Arizona actually amends its law to tie voting to proof of citizenship. At least until the preclearance provisions of the Voting Rights Act are struck down — which might be this month — Arizona would have to get approval for this change, which would be much harder under the Obama Justice Department than it was when the current provision was approved by the Bush administration. In theory, Congress could respond by overriding that requirement, but that assumes that such a bill could pass both houses, which seems unlikely.

But again, suppose that Congress acted or some federal agency or private group claimed that some provision of federal law pre-empted that requirement, just as the Motor Voter Law did for the federal registration form. That would raise an interesting constitutional question that was the basis for the dissents in this case. The issue arises because Article I, § 4 of the Constitution allows Congress to make rules regarding “The Times, Places and Manner” of holding congressional elections, whereas Article I, § 2 and the 17th Amendment provide that the qualifications for voters in elections for the House and Senate shall be set by the states, not Congress. The dissents in the recent Supreme Court decision saw the law tying registration to proof of citizenship as a qualification to vote, which Congress may not affect. The majority disagreed, and in my view has the better of the argument. But having to prove citizenship to vote is a lot closer to a qualification than is proving it to register. Thus, if Congress passed a law saying that a statement under oath was enough, or allowing proof by means in addition to what Arizona provides, including having voted for 10 or 20 years without objection, such a law might be argued to violate Arizona’s right to set voter qualifications. On the other hand, such a law might be defended on the ground that it deals with the “Manner” of conducting a federal election, not who is eligible to vote.

There is another avenue by which federal law could pre-empt contrary state law, even if a provision is found to be a voter qualification. In the 1970 amendments to the Voting Rights Act Congress lowered the age for voting in federal and state elections from 21 to 18; outlawed literacy tests; and nullified certain state laws that imposed significant durational residence requirements before allowing new arrivals to vote in presidential elections. In Oregon v. Mitchell, the Supreme Court upheld the second and third of those provisions and sustained the first as applied to federal, but not state elections. The majority in footnote 8 in the recent Arizona ruling discounted that decision and suggested that the qualifications clauses might invalidate a law telling a state what proof it may and may not use for a voter to establish citizenship. Given the issues in today’s decision, the majority was not called upon to overrule Mitchell, which also relied on the 14th Amendment.

There is a further potential basis for congressional intervention in this area. The qualifications clauses apply only to elections for Congress, not for the president, which are governed by Article II, § 1, which creates the Electoral College. States are free to choose their delegates to the Electoral College as they see fit, and originally most did not use popular elections, which explains why there is no qualifications clause barrier to overcome if Congress enacted a law applicable only to presidential elections. Technically, such a federal law could not apply to congressional, let alone state elections, but, as is true for the Motor Voter Law which literally governs only federal elections, its practical impact would be to make it applicable to all elections, since most states will not be willing to spend the time and money to set up different systems for different elections being conducted on the same day at the same time and in the same place.

Whether the Supreme Court will have to answer any of these questions is in the first instance up to Arizona if it tries to resurrect proof of citizenship by other means. However, when legislators and others are contemplating such a response, they should ask themselves how big are the problems with claims of false citizenship, what costs will be incurred in defending their response, and how will that play out as the country is having a much larger debate about how to cure the problem of illegal immigrants and integrate them into our society. Whether fairly or not, Arizona’s law was perceived as anti-Hispanic, and some politicians may want to rethink whether that’s where they still want to be today.

Alan B. Morrison is the Lerner Family Associate Dean for Public Interest & Public Service Law at George Washington University Law School, where he teaches constitutional law and, in some years, election law.