Since Republicans won control of many statehouses last November, more than a dozen states have passed laws requiring voters to show photo identification at polls, cutting back early voting periods or imposing new restrictions on voter registration drives.

With a presidential campaign swinging into high gear, the question being asked is how much of an impact all of these new laws will have on the 2012 race.

State officials, political parties and voting experts have all said that the impact could be sizable. Now, a new study to be released Monday by the Brennan Center for Justice at New York University School of Law has tried to tally just how many voters stand to be affected.

The center, which has studied the new laws and opposed some of them in court and other venues, analyzed 19 laws that passed and 2 executive orders that were issued in 14 states this year, and concluded that they “could make it significantly harder for more than five million eligible voters to cast ballots in 2012.”

Despite decades of progress, this year’s Republican-backed wave of voting restrictions has demonstrated that the fundamental right to vote is still subject to partisan manipulation. The most common new requirement, that citizens obtain and display unexpired government-issued photo identification before entering the voting booth, was advanced in 35 states and passed by Republican legislatures in Alabama, Minnesota, Missouri and nine other states — despite the fact that as many as 25 percent of African-Americans lack acceptable identification.

Having fought for voting rights as a student, I am especially troubled that these laws disproportionately affect young voters. Students at state universities in Wisconsin cannot vote using their current IDs (because the new law requires the cards to have signatures, which those do not). South Carolina prohibits the use of student IDs altogether. Texas also rejects student IDs, but allows voting by those who have a license to carry a concealed handgun. These schemes are clearly crafted to affect not just how we vote, but who votes.

Conservative proponents have argued for photo ID mandates by claiming that widespread voter impersonation exists in America, despite overwhelming evidence to the contrary. While defending its photo ID law before the Supreme Court, Indiana was unable to cite a single instance of actual voter impersonation at any point in its history. Likewise, in Kansas, there were far more reports of U.F.O. sightings than allegations of voter fraud in the past decade. These theories of systematic fraud are really unfounded fears being exploited to threaten the franchise.

Less than a year before the 2012 presidential voting begins, Republican legislatures and governors across the country are rewriting voting laws to make it much harder for the young, the poor and African-Americans — groups that typically vote Democratic — to cast a ballot.

Spreading fear of a nonexistent flood of voter fraud, they are demanding that citizens be required to show a government-issued identification before they are allowed to vote. Republicans have been pushing these changes for years, but now more than two-thirds of the states have adopted or are considering such laws. The Advancement Project, an advocacy group of civil rights lawyers, correctly describes the push as “the largest legislative effort to scale back voting rights in a century.”

Anyone who has stood on the long lines at a motor vehicle office knows that it isn’t easy to get such documents. For working people, it could mean giving up a day’s wages.