We may never know how many non-citizens voted illegally on November 4.

A report on FOX affiliate WFLD-TV in Chicago that aired just before the election showed how easy it is for non-citizens to register: They used a hidden camera in a DMV office to show a Chinese citizen illegally registering to vote as she obtained a driver's license.

However, American citizens recently won a significant victory that could help ensure the integrity of future elections and prevent non-citizens, both legal and illegal, from stealing their votes. On August 20, a federal district court judge in Arizona upheld the Arizona Taxpayer and Citizen Protection Act, i.e., Proposition 200, which requires proof of citizenship to register and proof of identification to vote in person.

Despite the fact that almost every elected official in Arizona opposed Proposition 200 in 2004, Arizona citizens passed it overwhelmingly. In typical fashion, the plaintiffs (including the usual suspects: ACORN, Common Cause, the League of Women Voters, LULAC, and People for the American Way) claimed every possible violation of voting and civil rights laws, as well as the Constitution.

There are numerous reported cases of non-citizens registering and voting in American elections. We basically have an honor system in which we assume that individuals who aren't U.S. citizens will follow the law. Of course, there is also evidence that some third-party organizations deliberately turn a blind eye to the citizenship of the individuals they register and that even state officials, particularly at DMV offices, register individuals they know aren't citizens. I recently received a copy of a voter application in which the applicant honestly answered that she wasn't a U.S. citizen. Yet Philadelphia election officials registered her anyway, and she voted in the 2004 election.

Cases like this show that our honor system has failed. Arizona's new state requirement is the only sure way of preventing non-citizens from registering to vote.

Even with twice the number of usual suspects acting as plaintiffs in Arizona, they still couldn't show the court that any substantial burden was placed on voters to comply with this citizenship requirement. Applicants can register with a driver's license, birth certificate, passport, naturalization certificate (or just the alien registration number on the certificate), tribal identification, or any other document accepted by the federal government to prove citizenship. As in Georgia and Indiana, the Arizona plaintiffs could produce no one who either lacked an ID or couldn't easily obtain one.

In fact, the named plaintiff, Jesus Gonzalez, a naturalized Mexican-American, not only had a copy of his naturalization certificate, he even had a U.S. passport. The plaintiffs' attorneys were reduced to making the ludicrous claim that having to provide election officials with an alien registration number, which is verified by the state through the electronic SAVE system also used by employers, was an unconstitutional "burden" on the right to vote. As the court rightfully held, naturalized citizens obviously "do not suffer an excessive burden due to Proposition 200."

The Arizona plaintiffs made one of the nonsensical claims consistently made by opponents of voter ID-that having to prove citizenship and show ID would reduce turnout in elections. The judge held that the findings of the plaintiffs' expert were unreliable, but even that expert asserted that only 2 percent of Arizona's eligible population didn't have proof of citizenship. Another expert found that the possible reduction in Latino turnout in the 2006 election caused by the citizenship requirement was only 0.06 percent. Out of over 3.1 million ballots cast in the 2006 primary, the 2006 general election, and the 2008 presidential primary, only 0.13 percent of the ballots weren't counted because voters couldn't produce ID.

Echoing the Supreme Court's decision in the Indiana voter ID case, the Arizona court found that preventing voter fraud was an important governmental interest that justified the proof of citizenship requirement, particularly when the state had actual evidence of non-citizens who had registered and voted illegally in Arizona in past elections. The law was also an important safeguard in protecting voter confidence in the election process.

Legislators in numerous states have been watching the Arizona case closely. Now that a federal court has found a proof of citizenship requirement lawful, they hopefully will pass similar measures. Only if other states follow Arizona's example will we know for sure in 2012 that only American citizens are deciding who the next president will be.

Hans A. von Spakovsky is a visiting legal scholar at the Heritage Foundation and a former member of the Federal Election Commission. He was Counsel to the Assistant Attorney General for Civil Rights at the U.S. Department of Justice from 2002 to 2005.