Teresa Sharp is fifty-three years old and has lived in a modest single-family house on Millsdale Street, in a suburb of Cincinnati, for nearly thirty-three years. A lifelong Democrat, she has voted in every Presidential election since she turned eighteen. So she was agitated when an official summons from the Hamilton County Board of Elections arrived in the mail last month. Hamilton County, which includes Cincinnati, is one of the most populous regions of the most fiercely contested state in the 2012 election. No Republican candidate has ever won the Presidency without carrying Ohio, and recent polls show Barack Obama and Mitt Romney almost even in the state. Every vote may matter, including those cast by the seven members of the Sharp family—Teresa, her husband, four grown children, and an elderly aunt—living in the Millsdale Street house.

The letter, which cited arcane legal statutes and was printed on government letterhead, was dated September 4th. “You are hereby notified that your right to vote has been challenged by a qualified elector,” it said. “The Hamilton County Board of Elections has scheduled a hearing regarding your right to vote on Monday, September 10th, 2012, at 8:30 A.M. . . . You have the right to appear and testify, call witnesses and be represented by counsel.”

“My first thought was, Oh, no!” Sharp, who is African-American, said. “They ain’t messing with us poor black folks! Who is challenging my right to vote?”

The answer to Sharp’s question is that a new watchdog group, the Ohio Voter Integrity Project, which polices voter-registration rolls in search of “electoral irregularities,” raised questions about her eligibility after consulting a government-compiled list of local properties and mistakenly identifying her house as a vacant lot.

The Sharp household had first been identified as suspicious by computer software that had been provided to the Ohio Voter Integrity Project by a national organization called True the Vote. The software, which has been distributed to similar groups around the country, is used to flag certain households, including those with six or more registered voters. This approach inevitably pinpoints many lower-income residents, students, and extended families.

True the Vote, which was founded in 2009 and is based in Houston, describes itself as a nonprofit organization, created “by citizens for citizens,” that aims to protect “the rights of legitimate voters, regardless of their political party.” Although the group has a spontaneous grassroots aura, it was founded by a local Tea Party activist, Catherine Engelbrecht, and from the start it has received guidance from intensely partisan election lawyers and political operatives, who have spent years stoking fear about election fraud. This cohort—which Roll Call has called the “voter fraud brain trust”—has filed lawsuits, released studies, testified before Congress, and written op-ed columns and books. Since 2011, the effort has spurred legislative initiatives in thirty-seven states to require photo identification to vote.

Engelbrecht has received especially valuable counsel from one member of the group: Hans von Spakovsky. A Republican lawyer who served in the Bush Administration, he is now a senior legal fellow at the Heritage Foundation, the conservative think tank. “Hans is very, very helpful,” Engelbrecht said. “He’s one of the senior advisers on our advisory council.” Von Spakovsky, who frequently appears on Fox News, is the co-author, with the columnist John Fund, of the recent book “Who’s Counting?,” which argues that America is facing an electoral-security crisis. “Election fraud, whether it’s phony voter registrations, illegal absentee ballots, vote-buying, shady recounts, or old-fashioned ballot-box stuffing, can be found in every part of the United States,” they write. The book connects these modern threats with sordid episodes from the American past: crooked inner-city machines, corrupt black bosses in the Deep South. Von Spakovsky and Fund conclude that electoral fraud is a “spreading” danger, and declare that True the Vote serves “an obvious need.”

Mainstream election experts say that Spakovsky has had an improbably large impact. Richard L. Hasen, a law professor at the University of California at Irvine, and the author of a recent book, “The Voting Wars,” says, “Before 2000, there were some rumblings about Democratic voter fraud, but it really wasn’t part of the main discourse. But thanks to von Spakovsky and the flame-fanning of a few others, the myth that Democratic voter fraud is common, and that it helps Democrats win elections, has become part of the Republican orthodoxy.” In December, Reince Priebus, the chairman of the Republican National Committee, wrote, “Election fraud is a real and persistent threat to our electoral system.” He accused Democrats of “standing up for potential fraud—presumably because ending it would disenfranchise at least two of its core constituencies: the deceased and double-voters.” Hasen believes that Democrats, for their part, have made exaggerated claims about the number of voters who may be disenfranchised by Republican election-security measures. But he regards the conservative alarmists as more successful. “Their job is really done,” Hasen says. “It’s common now to assert that there is a need for voter I.D.s, even without any evidence.”

In Hamilton County alone, the new citizens’ groups have challenged more than a thousand names since March. Some challenges, such as those aiming to disqualify college students who failed to include their dorm-room numbers on their registration forms, were tossed out immediately. But the board accepted nearly two hundred challenges, including those to twenty-six voters registered at a trailer park that no longer existed.

In Ohio, if voters whose eligibility has been challenged come to the polls in November, they may be forced to use a provisional ballot, which will be counted only if officials sanction it—after Election Day. Some experts worry that voters who have been needlessly challenged will feel too intimidated even to show up. “People have other things to do with their lives than respond to inaccurate complaints accusing them of being criminals,” Justin Levitt, a professor at Loyola Law School in Los Angeles, said.

Alex Triantafilou, a Republican member of the county’s Board of Elections, maintains that the challenges have been nonpartisan. But Caleb Faux, a Democrat on the board, says, “I don’t buy it. The True the Vote people are clearly going after Democratic voters: African-Americans, students, and other groups they think are likely to vote Democratic.”

Von Spakovsky recently sat down with me in a conference room at the Heritage Foundation, wearing rimless eyeglasses and a sports jacket with a crisp white pocket square. In our conversation, and in later phone calls and e-mails, he expressed himself with lawyerly reserve. He said of True the Vote and its affiliates, “They’re doing a great job.” Earlier this year, he noted, the Pew Center on the States found that more than 1.8 million people who had died were still registered to vote in America, and that 2.75 million people were registered to vote in multiple states. How many of these errors translate into fraudulent votes? “It is impossible to answer,” he said. “We don’t have the tools in place.” But he cited a 2000 investigation, by the Atlanta Journal-Constitution, of voting records in Georgia over the previous two decades; the paper reported that it had turned up fifty-four hundred instances of dead people being recorded as having voted. “That seems pretty substantial to me,” he said.