Already, 25 states, including Missouri, require some form of identification at the polls. Seven of those states require or can request photo ID. More states may soon decide to require photo ID now that the Supreme Court has upheld the practice. Democrats have already criticized these requirements as implicitly intended to keep lower-income voters from the polls, and are likely to fight even more fiercely now that the requirements are expanding to include immigration status.  “Three forces are converging on the issue: security, immigration and election verification,” said Dr. Robert A. Pastor, co-director of the Center for Democracy and Election Management at American University in Washington. This convergence, he said, partly explains why such measures are likely to become more popular and why they will make election administration, which is already a highly partisan issue, even more heated and litigious.  The Missouri secretary of state, Robin Carnahan, a Democrat who opposes the measure, estimated that it could disenfranchise up to 240,000 registered voters who would be unable to prove their citizenship.  In most of the states that require identification, voters can use utility bills, paychecks, driver’s licenses or student or military ID cards to prove their identity. In the Democratic primary election last week in Indiana, several nuns were denied ballots because they lacked the required photo IDs.  Measures requiring proof of citizenship raise the bar higher because they offer fewer options for documentation. In most cases, aspiring voters would have to produce an original birth certificate, naturalization papers or a passport. Arizona and Missouri, along with some other states, now show whether a driver is a citizen on the face of a driver’s license, and within a few years all states will be required by the federal government to restrict licenses to legal residents.  Critics say that when this level of documentation is applied to voting, it becomes more difficult for the poor, disabled, elderly and minorities to participate in the political process.  “Everyone has been focusing on voter ID laws generally, but the most pernicious measures and the ones that really promise to prevent the most eligible voters from voting is what we see in Arizona and now in Missouri,” said Jon Greenbaum, a former voting rights official at the Department of Justice and now the director of the voting rights project at the Lawyers’ Committee for Civil Rights Under Law, a liberal advocacy group.  Aside from its immediacy, the action by Missouri is important because it has been a crucial swing state in recent presidential elections, with outcomes often decided by a razor-thin margin.  Supporters of the measures cite growing concerns that illegal immigrants will try to vote. They say proof of citizenship measures are an important way to improve the accuracy of registration rolls and the overall voter confidence in the process.  State Representative Stanley Cox, a Republican from Sedalia and the sponsor of the amendment, said that the Missouri Constitution already required voters to be citizens and that his amendment was simply meant to better enforce that requirement.  “The requirements we have right now are totally inadequate,” Mr. Cox said. “You can present a utility bill, and that doesn’t prove anything. I could sit here with my nice photocopier and create a thousand utility bills with different names on them.”  From October 2002 to September 2005, the Justice Department indicted 40 voters for registration fraud or illegal voting, 21 of whom were noncitizens, according to department records.  In 2006, the Missouri legislature passed a photo identification bill that the State Supreme Court later ruled unconstitutional because it placed too much of a burden on voters. It was that ruling that has spurred state lawmakers to try to change the constitution.  The proposed amendment does not require the signature of the governor but would need to be approved by the voters in the state’s August primary in the governor’s race to take effect before the presidential election.  If passed this week, the amendment clears the way for a pending bill that would require some kind of identification in order to prove citizenship and to register to vote. But many questions about the bill — like whether current registered voters will have to obtain a new form of identification — have not been resolved.  Lillie Lewis, a voter who lives in St. Louis and spoke at a news conference last week organized to oppose the amendment, said she already had a difficult time trying to get a photo ID from the state, which asked her for a birth certificate. Ms. Lewis, who was born in Mississippi and said she was 78 years old, said officials of that state sent her a letter stating that they had no record of her birth.  “That’s downright wrong,” Ms. Lewis said. “I have voted in almost all of the presidential races going back I can’t remember how long, but if they tell me I need a passport or birth certificate that’ll be the end of that.”  A 2006 federal rule intended to keep illegal immigrants from receiving Medicaid was widely criticized by state officials for shutting out tens of thousands of United States citizens who were unable to find birth certificates or other documents proving their citizenship.  Supporters of citizenship requirements, however, say the threat of voting by illegal immigrants is real. Thor Hearne, a lawyer from Missouri who has been a strong advocate for voter ID laws, cited a California congressional race in 1996 in which a Republican, Bob Dornan, was narrowly defeated. Mr. Dornan contested the results, claiming that illegal immigrants had voted.  After a 14-month investigation by state, county and federal officials, a panel concluded that up to 624 noncitizens may have registered to vote. The report came to no firm determination of whether any of those people had actually voted.  Mr. Hearne said the requirement would not pose a significant hardship on voters.  “There were a lot of the same alarmist charges regarding Indiana voter ID law and how it would disenfranchise so many people,” Mr. Hearne said, “and those allegations were not accepted by the Supreme Court.” He added that if states actively provided a free form of identification proving citizenship, the number of people who would be disenfranchised would be very low.  “To those who have spent great energy opposing some of the voter registration or voter identification requirements, I would say their energy would be much better spent working toward trying to provide identifications to those who need them or assisting these people with getting registered,” Mr. Hearne said.  But organizations working in Arizona say they are doing just that and running into problems.  “The requirement is having a devastating effect on our voter registration work in Latino communities because so many citizens simply don’t have a passport or original birth certificate,” said Michael Slater, deputy director of Project Vote, a liberal advocacy group that is working with Acorn, a national organizing group, to sign up new voters in Arizona.  But Arizona officials say the measure is broadly popular in the state  “The voters of Arizona feel strongly about proof of citizenship when registering to vote as a basic eligibility requirement,” said the secretary of state, Jan Brewer, a Republican, testifying before Congress in March.  A version of this article appears in print on , on Page A1 of the New York edition with the headline: VOTER ID BATTLE SHIFTS TO PROOF OF CITIZENSHIP. Order Reprints| Today's Paper|Subscribe
Supporters of a measure in Missouri cite concerns about illegal immigrants voting, but critics say tens of thousands of legal residents could be disenfranchised.