So what are these laws?
They are measures intended to ensure that a registered voter is who he says he is and not an impersonator trying to cast a ballot in someone else’s name. The laws, most of which have been passed in the last several years, require that registered voters show ID before they’re allowed to vote. Exactly what they need to show varies. Some states require a government-issued photo, while in others a current utility bill or bank statement is sufficient.
As a registered voter, I thought I always had to supply some form of ID during an election.
Not quite. Per federal law , first-time voters who registered by mail must present a photo ID or copy of a current bill or bank statement. Some states generally advise voters bring some form of photo ID . But prior to the 2006 election, no state ever required a voter to produce a government-issued photo ID as a condition to voting. Indiana in 2006 became the first state to enact a strict photo ID law, a law that was upheld  two years later by the U.S. Supreme Court.
Why are these voter ID laws so strongly opposed?
Voting law opponents contend these laws disproportionately affect elderly, minority and low-income groups that tend to vote Democratic. Obtaining photo ID can be costly and burdensome, with even free state ID requiring documents like a birth certificate that can cost up to $25 in some places. According to a study  from NYU’s Brennan Center, 11 percent of voting-age citizens lack necessary photo ID while many people in rural areas have trouble accessing ID offices. During closing arguments in a recent case over Texas’s voter ID law, a lawyer for the state  brushed aside these obstacles as the “reality to life of choosing to live in that part of Texas.”
Attorney General Eric Holder and others have compared  the laws to a poll tax , in which Southern states during the Jim Crow era imposed voting fees, which discouraged blacks, and even some poor whites — until the passage of grandfather clauses  — from voting.
Given the sometimes costly steps required to obtain needed documents today, legal scholars argue  that photo ID laws create a new “financial barrier to the ballot box.”
Just how well-founded are fears of voter fraud?
There have been only a small number of fraud cases resulting in a conviction. A New York Times analysis from 2007  identified 120 cases filed by the Justice Department over five years. These cases, many of which stemmed from mistakenly filled registration forms or misunderstanding over voter eligibility, resulted in 86 convictions.
There are “very few documented cases,” said UC-Irvine professor and election law specialist Rick Hasen. “When you do see election fraud, it invariably involves election officials taking steps to change election results or it involves absentee ballots which voter ID laws can’t prevent,” he said.
An analysis by News21, a national investigative reporting project, identified  10 voter impersonation cases out of 2,068 alleged election fraud cases since 2000 – or one out of every 15 million prospective voters.
One of the most vocal supporters of strict voter ID laws, Texas Attorney General Greg Abbott, told the Houston Chronicle  earlier this month that his office has prosecuted about 50 cases of voter fraud in recent years. “I know for a fact that voter fraud is real, that it must be stopped, and that voter id is one way to prevent cheating at the ballot box and ensure integrity in the electoral system,” he told the paper. Abbott’s office did not immediately respond to ProPublica’s request for comment.
How many voters might be turned away or dissuaded by the laws, and could they really affect the election?
It’s not clear.
According to the Brennan Center, about 11 percent of U.S. citizens, or roughly 21 million citizens, don’t have government-issued photo ID. This figure doesn’t represent all voters likely to vote, just those eligible to vote.
In late September, an analysis  by Reuters and research firm Ipsos of data culled from 20,000 voter interviews found that those lacking proper ID were less likely to vote anyway, “regardless of state law changes.”
Among those who said they were “certain to vote,” only 1 percent said they did not have proper ID while another 1 percent said they were uncertain whether they had the proper ID.
The analysis also found that those who lack valid photo ID tended to be young people, those without college educations, Hispanics and the poor.
State figures also can be hard to nail down. In Pennsylvania, nearly 760,000 registered voters, or 9.2 percent of the state’s 8.2 million voter base, don’t own state-issued ID cards, according to an analysis of state records  by the Philadelphia Inquirer. State officials, on the other hand, place this number at between 80,000 and 90,000.
In Indiana and Georgia, states with the earliest versions of photo ID laws, about 1,300 provisional votes were discarded in the 2008 general election, later analysis  has revealed.
As for the potential effect on the election, one analysis by Nate Silver at the New York Times’ FiveThirtyEight blog estimates they could decrease voter turnout anywhere between 0.8 and 2.4 percent . It doesn’t sound like a very wide margin, but it all depends on the electoral landscape .
“We don’t know exactly how much these news laws will affect turnout or skew turnout in favor of Republicans,” said Hasen, author of the recently released  The Voting Wars: From Florida 2000 to the Next Election Meltdown. “But there’s no question that in a very close election, they could be enough to make a difference in the outcome.”
When did voter ID laws get passed — and which states have the strictest ones?
The first such law was passed as early as 2003 , but momentum has picked up in recent years. In 2011 alone , legislators in 34 states introduced bills requiring voters show photo ID — 14 of those states already had existing voter ID laws but lawmakers sought to toughen statutes, mainly to require proof of photo identification.
The National Conference of State Legislatures has a helpful breakdown  of states’ voter ID laws and how they vary.
Indiana, Georgia, Tennessee, Kansas and Pennsylvania have the toughest versions. These states won’t allow voters to cast a regular ballot without first showing valid photo ID. Other states with photo ID laws offer some more flexibility by providing voters with several alternatives.
What happens if a voter can’t show valid photo ID in these states?
These voters are entitled to a provisional ballot . To ensure their votes count, however, they must produce the mandatory ID within a certain time frame and affirm in person or writing they are the same individual who filled out a temporary ballot on Election Day. The time limits vary: They range anywhere from up to three days after the election (Georgia) to noon the Monday after the election (Indiana).
Are there any exceptions to the photo ID requirement?
Yes. Indigency or religious objections to being photographed. But these exceptions don’t automatically grant a voter the ability to cast a regular ballot: In Pennsylvania  and Indiana , voters will be given a provisional ballot and must sign an affidavit for their exemption within the given time frame. For a more specific breakdown of all exceptions, see this state-by-state summary .
Why is the Justice Department getting involved in some cases?
Because of Section 5 of the Voting Rights Act , which requires that states with a history of discrimination receive preclearance before making changes to voting laws. Texas  and South Carolina  passed strict photo ID laws in 2011 but were refused preclearance by the DOJ, which argued that these laws could suppress turnout among minority voters. Texas went to court seeking judicial preclearance from a federal district court; in August, a three-judge panel of the U.S. District Court for the District of Columbia blocked the law . South Carolina has presented  arguments before the same court.
What about challenges to the laws?
On Aug. 15, a Pennsylvania judge shot down  an attempt to attempt to block the state’s voter ID law. The plaintiffs appealed. On Sept. 18, the Pennsylvania Supreme Court, by a 4-2 vote, vacated  the judge’s order and returned the case for further review. The justices asked the trial judge to assess whether voters could obtain state-issued photo ID without difficulty in the short time remaining before the November general election. If the judge could not be convinced voters wouldn’t be disenfranchised, the justices wrote, the law should be temporarily blocked.
In an Oct. 2 ruling,  Commonwealth Court Judge Robert Simpson did just that. He wrote that he was “not still convinced” that voters yet to obtain photo ID wouldn’t be disenfranchised as a result of the new law. He blocked it from taking effect, but only for the upcoming November 6 election. Additionally, the judge’s ruling still permits Pennsylvania election officials to request photo ID from registered voters this election, just not prevent anyone from casting a regular ballot if they’re unable to produce one.
As we’ve reported, other judges have also ruled in favor of other states’ voter ID laws. Here’s a rundown of the rulings. 
The DOJ is also investigating many of the states’ laws, including Pennsylvania’s photo ID law. As first reported by Talking Points Memo , the DOJ’s Civil Rights Division sent the state’s chief election official a letter  Monday afternoon requesting 16 separate items, including the state’s complete voter registration list, any documents supporting the governor’s prior assurance that “99 percent” of the state’s eligible voters already have acceptable photo ID, any papers to prove the state is prepared to provide registered voters with ID cards free of charge upon oath or affirmation, and any studies that inform state officials of the “demographic characteristics” of residents who lack valid voter ID.
The DOJ letter states it needs these documents within 30 days to evaluate the state’s compliance with Section 2 of the Voting Rights Act , which forbids voting practices that discriminate on the basis of race, color, or membership in a language minority group.
Have any states attempted to enact strict voter ID laws but so far been unsuccessful?
Yes. In Wisconsin, two judges have blocked enforcement  of the state’s photo ID law. The state attorney general has asked  the Wisconsin Supreme Court to intervene and reinstate the law before the November election. Meantime, Democratic governors in Minnesota, Missouri, New Hampshire and North Carolina have vetoed strict photo ID bills  passed by their Republican-led legislatures last year.
Are there other voter ID laws in effect that ask for but don’t necessarily require photo ID?
Yes. In these so-called “non-strict photo ID states” — Florida, Louisiana, Michigan, Idaho, South Dakota and Hawaii — individuals are requested to show photo ID but can still vote if they don’t have one. Instead, they may be asked to sign affidavits affirming their identity or provide a signature that will be compared with those in registration records.
Why has there been such a recent surge in voter ID legislation around the country?
This report  by NYU’s Brennan Center for Justice cites primarily big Republican gains in the 2010 midterms which turned voter ID laws into a “major legislative priority.” Aside from Rhode Island , all voter ID legislation has been introduced  by Republican-majority legislatures.
News21 also has this report  on the close affiliation between the bills’ sponsors and the conservative nonprofit group, American Legislative Exchange Council (ALEC).
Republican figures have championed such laws. For instance, Mike Turzai, majority leader of the Pennsylvania House of Representatives, recently praised the state’s legislative accomplishments  at a Republican State Committee meeting last month. “Voter ID, which is gonna allow Governor Romney to win the state of Pennsylvania, done,” he said.
A spokesman for Turzai, Steve Miskin, told ProPublica that Turzai was “mischaracterized” by the press. “For the first time in many years, you’re going to have a relatively level playing field in the presidential elections” as the result of these new laws,” Miskin said. “With all things equal, a Republican presidential nominee in Pennsylvania has a chance.”
Correction August 20, 2012: An earlier version of this story incorrectly stated “voting law advocates contend these laws disproportionately affect elderly, minority and low-income groups that tend to vote Democratic.” It’s voting law opponents who make that contention.
Correction July 24, 2012: An earlier version of this story said Texas went to federal court to challenge the DOJ’s denial of preclearance. In fact, Texas filed a lawsuit seeking preclearance from the federal district court two months before the DOJ announced its decision. Also, some states require a government-issued photo that does not have to come from the federal government as first detailed.
Clarification Sept. 25, 2012: This post has been clarified to reflect details about who was discouraged from voting under a poll tax.