Opponents "argue that Arizona should not be permitted to request evidence of citizenship when someone registers to vote, but should instead rely on the person's sworn statement that he or she is a citizen," Arizona Attorney General Thomas C. Horne said in court papers.
"The fallacy in that is that someone who is willing to vote illegally will be willing to sign a false statement. What (opponents) are urging is that there should be nothing more than an honor system to assure that registered voters are citizens. That was not acceptable to the people of Arizona."
The Arizona proposition was enacted into law with 55 percent of the vote.
This is the second voting issue the high court is tackling this session. Last month, several justices voiced deep skepticism about whether a section of the Voting Rights Act of 1965, a law that has helped millions of minorities exercise their right to vote, especially in areas of the Deep South, was still needed.
This case involves laws of more recent vintage.
The federal "Motor Voter" law, enacted in 1993 to expand voter registration, allows would-be voters to fill out a mail-in voter registration card and swear they are citizens under penalty of perjury, but it doesn't require them to show proof.
Under Proposition 200 approved in 2004, Arizona officials require an Arizona driver's license issued after 1996, a U.S. birth certificate, a passport or other similar document, or the state will reject the federal registration application form.
This requirement applies only to people who seek to register using the federal mail-in form. Arizona has its own form and an online system to register when renewing a driver's license. The court ruling did not affect proof of citizenship requirements using the state forms.
State officials say more than 90 percent of those Arizonans applying to vote using the federal form will be able to simply write down their driver's license number, and all naturalized citizens simply will be able to write down their naturalization number without needed additional documents.
Former Arizona Senate President Russell Pearce, a leading Republican proponent of Proposition 200, strongly disputed claims that Arizona doesn't have voter fraud problems. "They turn a blind eye," Pearce said of the state's election officials.
But Karen Osborne, elections director for Maricopa County, where nearly 60 percent of Arizona's voters live, said voter fraud is rare, and even rarer among illegal immigrants.
"That just does not seem to be an issue," Osborne said of the claim that illegal immigrants are voting. "They did not want to come out of the shadows. They don't want to be involved with the government."
The main legal question facing the justices is whether the federal law trumps Arizona's law. A 10-member panel of the 9th Circuit in San Francisco said it did.
The appeals court issued multiple rulings in this case, with a three-judge panel initially siding with Arizona. A second panel that included retired Supreme Court Justice Sandra Day O'Connor, who from time to time sits on appeals courts, reversed course and blocked the registration requirement. The full court then did the same, and that decision will be reviewed by the justices in Washington.
The case is 12-71, Arizona v. Inter Tribal Council of Arizona, Inc.
Billeaud reported from Phoenix.
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