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The Supreme Court will hear arguments later today on a challenge to Arizona's Proposition 200, a 2004 measure that required proof of citizenship to vote. If the Court upholds the measure, it could significantly curtail the Latino vote for years.

Prop. 200 requires that voters show a recent drivers license, passport, or birth certificate if registering to vote using the federal government's form. The Associated Press reports that the move had an immediate effect on registration.

Opponents of the Arizona provision say they've counted more than 31,000 potentially legal voters in Arizona who easily could have registered before Proposition 200 but who were blocked initially by the law in the 20 months after it passed in 2004. They say about 20 percent of those thwarted were Latino.

How those 31,000 voters were blocked despite being legally eligible to vote is explained a bit more in a friend-of-the-court filing. 11,000 attempted to register at least twice before doing so successfully. An expert for the plaintiffs challenging Prop. 200 testified that another 20,000 eligible voters didn't register because of the "onerous requirements" of the proposition and roughly 20 percent were Latino. "Far from allowing straightforward mail-in registration, these onerous requirements can often be met only through an in-person appearance at a local governmental office to obtain and provide the requisite documentation," reads the Latino Justice brief. A later report from the expert cited in that case puts the number at over 38,000 affected voters

If the Supreme Court upholds the legality of Prop. 200, it is, in effect, allowing a slightly more difficult path to the ballot box for voters — largely voters from lower income communities and communities of color.

Like much of the rest of the country, Arizona is changing. As of early last year, 30 percent of the state was Latino; by 2020, it's expected to be majority-minority, meaning that whites will comprise less than 50 percent of the population.

That demographic shift has political implications. In 2008, Latino voters preferred Obama by 15 percent — in John McCain's home state. In 2012, Latino voters nationally chose Obama by 44 points. Curtailing the Latino vote, at least for now, means to some extent curtailing the Democratic vote. And if the Court allows Prop. 200 to stand, it's likely that other states with conservative legislatures would enact similar measures, as Talking Points Memo notes.

The Court won't be considering the political ramifications of such moves. It will, instead, be judging whether or not Prop. 200 inappropriately trumps federal election law by imposing an additional requirement for voters beyond what exists under the federal National Voter Registration Act — the 1993 "motor voter" bill. According to the Arizona Republic's timeline of the proposition's path to the court, last April, the 9th Circuit Court determined that another element of Prop. 200, which mandates that voters show ID at the polls, could stand. In a parallel 9-2 decision, it threw out the citizenship documentation requirement for federal registrations — but not for state registration forms, which are the sole province of the state. This dual system is what was in effect for last fall's presidential election: proof of citizenship for those registering through Arizona, none needed to register through the federal government.

What's not clear is what benefit is obtained by the measure. The Associated Press quotes one of the measure's proponents.

Kathy McKee, who led the push to get the proposition on the ballot, said voter fraud, including by illegal immigrants, continues to be a problem in Arizona. "For people to conclude there is no problem is just shallow logic," McKee said.

One person employing shallow logic is Karen Osborne.

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."

Osborne's anecdotal experience is backed by data. Since 2000, there have been 400 cases of fraudulent registration among the millions of registered voters nationwide. Nor would any concerns among Republicans be warranted in Arizona: the state has two Republican senators, four of its nine House members are Republican, and Republicans control both sides of the state legislature.

The effect of the Latino voting bloc may be seen most clearly next year, however, when the state's staunchly anti-immigration governor Jan Brewer is up for reelection. A poll taken last February suggested that 60 percent of Latinos held an unfavorable opinion of Brewer, compared to 50 percent approval among white voters. If it's close race next year, Brewer's reelection may come down to how many Latinos go to the polls. Which may come down to the Supreme Court.

This article is from the archive of our partner The Wire.

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