It might as well be Harry Potter's invisible Knight Bus, because no one can prove it exists.
The bus has been repeatedly cited by True the Vote, a national group focused on voter fraud. Catherine Engelbrecht, the group's leader, told a gathering in July about buses carrying dozens of voters showing up at polling places during the recent Wisconsin recall election.
"Magically, all of them needed to register and vote at the same time," Ms. Engelbrecht said. "Do you think maybe they registered falsely under false pretenses? Probably so."
Weeks later, another True the Vote representative told a meeting of conservative women about a bus seen at a San Diego polling place in 2010 offloading people "who did not appear to be from this country."
Officials in both San Diego and Wisconsin said they had no evidence that the buses were real. "It's so stealthy that no one is ever able to get a picture and no one is able to get a license plate," said Reid Magney, a spokesman for the Wisconsin agency that oversees elections. In some versions the bus is from an Indian reservation; in others it is full of voters from Chicago or Detroit. "Pick your minority group," he said.
The buses are part of the election fraud gospel according to True the Vote, which is mobilizing a small army of volunteers to combat what it sees as a force out to subvert elections. Ms. Engelbrecht's July speech in Montana was titled "Voter Fraud: The Plot to Undermine American Democracy."
True the Vote's plan is to scrutinize the validity of voter registration rolls and voters who appear at the polls. Among those in their cross hairs: noncitizens who are registered to vote, those without proper identification, others who may be registered twice, and dead people. In Ohio and Indiana, True the Vote recently filed lawsuits to force officials to clean up voter rolls.
Efforts to tighten voter requirements have become a major issue in the presidential election. Over the last few years, many states have passed voter identification laws, and many of those are being challenged in court.
Now, a network of conservative groups is waging an aggressive campaign on the ground. In a report this month, the liberal-leaning organizations Common Cause and Demos cited True the Vote as the central player in this effort, which it called a threat to the fundamental right to vote.
"It is not about party or politics; it is about principle," Ms. Engelbrecht said.
While she portrays True the Vote as nonpartisan, it grew out of a Tea Party group, King Street Patriots, that she founded in Texas. An examination shows that it has worked closely with a variety of well-financed organizations, many unabashed in their desire to defeat President Obama.
A polished and provocative video, circulating among Tea Party activists, seeks to raise a "cavalry" to march on swing states and identifies True the Vote as a participant in the effort, called Code Red USA.
In the past year, Americans for Prosperity, an organization founded by the billionaire Koch brothers, and other Republican-leaning independent groups have sponsored meetings featuring Ms. Engelbrecht and other True the Vote speakers. A spokesman for Americans for Prosperity said that the group had hosted events including True the Vote speakers but that election integrity was not a focus of his group.
Election integrity has become a focus for other activists, including James E. O'Keefe III, a video producer known for his undercover stings of the now defunct community organizing group Acorn. He recently aimed his camera on North Carolina voters in what turned out to be a botched attempt to show that foreigners had registered.
Voter registration has occupied a contentious corner of American history for decades. The perception that voting is ripe for fraud stems in part from the condition of voter rolls in many jurisdictions. The Pew Center on the States issued a report in February finding that more than 1.8 million dead people remained on voter rolls and that about 2.8 million people were registered in more than one state. Another 12 million registrations contained flawed addresses, it said.
Even so, there have been few cases of widespread fraud, according to the Justice Department. A bipartisan commission in 2005 found little evidence of extensive fraud, even while recommending the use of voter identification.
While there have been some recent criminal cases involving local elections, the Justice Department said in a statement that the record has not shown that significant "voter impersonation fraud -- the type of fraud that many states claim their voter ID laws are aimed to prevent -- actually exists."
But Ms. Engelbrecht said, "Anyone who tells you that election integrity efforts are a solution looking for a problem is way misinformed."
True the Vote is now using proprietary software to accelerate the process of challenging voter registrations. It says its databases will ultimately contain all voter rolls in the country. Using computers, volunteers can check those rolls against driver's license records, property records and other databases, turning the process into an assembly line production.
But when True the Vote vetted petition signatures in Wisconsin's recall election, the state's Government Accountability Board reported that the process was "at best flawed." The group raised questions about thousands of signatures that the board deemed valid.
Roots of a Cause
Ms. Engelbrecht, who at 42 is younger than most of the Tea Party members she addresses around the country, said that until four years ago she was apolitical, a churchgoing mother of two who ran a successful oil field machinery business with her husband in Fort Bend County, Tex.
"Then in 2008, I don't know, something clicked," she said. "I saw our country headed in a direction that, for whatever reason -- it didn't hit me until 2008 -- this really threatens the future of our children."
The epiphany prompted Ms. Engelbrecht to work as a poll watcher in the 2009 local elections along with others in the King Street Patriots, the Tea Party group she founded. It was supposed to be a one-day assignment, but it crystallized the concerns of Ms. Engelbrecht and her fellow volunteers, who said they saw shenanigans including outright fraud. The group felt duty bound to continue its activities.
In Houston, the group targeted the Congressional district represented by Sheila Jackson Lee, a Democrat who is black. Ms. Engelbrecht said the group settled on Ms. Lee's district because thousands of addresses there housed six or more registered voters, which it took as an indication of inaccurate registrations. The methodology, which the group still uses, could disproportionately affect lower income families.
Volunteers spent five months analyzing 3,800 registrations in Ms. Lee's district, discovering more than 500 voters that the group said were problematic. More than 200 voters were registered at vacant lots, prompting Ms. Engelbrecht to later remark that those voters had a "Lord of the Rings Middle Earth sort of thing going on."
The reality was far less interesting.
"They had one particular case I remember very well," said Douglas Ray, the Harris County assistant attorney who represents the election registrar. "They had identified an address where eight or 10 people were registered to vote. There was no building there." Mr. Ray found out that the building had been torn down and that the people simply moved.
As a result of the organization's work in 2010, 400 to 500 voters were put on "suspense," forcing them to provide additional information verifying their addresses. By the fall 2010 election, volunteers again appeared to focus on minority neighborhoods, this time as election observers, Mr. Ray said.
"The first day of early voting, at many of the 37 locations, primarily in minority neighborhoods, dozens of poll watchers showed up sent by King Street Patriots," Mr. Ray said.
The influx of white election observers in black neighborhoods caused friction with voters and poll workers, bringing back memories of a time when racial intimidation at the polls was commonplace in the South, said Gerald M. Birnberg, a lawyer and former chairman of the Harris County Democratic Party. True the Vote has strongly denied that it has engaged in voter suppression.
"Whether that was the intention or just born of some innate paranoia is largely irrelevant," Mr. Birnberg said. "That's how it was perceived by people at the polls."
Working in Wisconsin
The boiling political caldron of Wisconsin was the next stop for True the Vote. It teamed up with two Tea Party organizations to review nearly one million signatures on petitions demanding the recall of Gov. Scott Walker, a Republican. The partnership called itself Verify the Recall.
"We have been hearing reports of duplicate signatures, questionable practices and downright fraud in the gubernatorial recall effort," Verify the Recall said in a pitch to volunteers. "The integrity of Wisconsin's elections and associated processes are at stake; free and honest elections -- the cornerstone of our political process -- are being threatened."
True the Vote began working in Wisconsin in 2011, the same year it received a $35,000 grant from the Lynde and Harry Bradley Foundation, which is based in Wisconsin and is a major backer of conservative causes, including Americans for Prosperity. The foundation's president and chief executive, Michael Grebe, was Mr. Walker's campaign chairman for his 2010 campaign and for the recall election, which he won.
Mr. Grebe said in an interview that the grant was for activities unrelated to the recall. He said the donation was ultimately returned because it was given on the premise that True the Vote would be granted tax-exempt status by the I.R.S., which Ms. Engelbrecht said has not happened despite several attempts.
Ms. Engelbrecht has said her goal was not to stop the recall election, which had been backed by labor unions, but to prove to those behind it "that unions cannot strong-arm America." She said thousands of volunteers helped enter petition signatures into a database, which was then analyzed by the group's software. Of the one million signatures, True the Vote said 63,038 were ineligible, 212,628 required further investigation and 584,489 were valid.
The accountability board concluded that about 900,000 signatures were valid and, in a memorandum reviewing True the Vote's work, criticized its methods.
For example: Mary Lee Smith signed her name Mary L. Smith and was deemed ineligible by the group.
Signatures deemed "out of state" included 13 from Milwaukee and three from Madison.
The group's software would not recognize abbreviations, so Wisconsin addresses like Stevens Point were flagged if "Pt." was used on the petition.
Signatures were struck for lack of a ZIP code.
While the board commended the group for encouraging "a strong level of civic engagement," it found that True the Vote's results "were significantly less accurate, complete and reliable than the review and analysis completed by the G.A.B."
On Election Day, poll watchers appeared to have slowed voting to a crawl at Lawrence University in Appleton, where some students were attempting to register and vote on the same day.
Charlene Peterson, the city clerk in Appleton, said three election observers, including one from True the Vote, were so disruptive that she gave them two warnings.
"They were making challenges of certain kinds and just kind of in physical contact with some of the poll workers, leaning over them, checking and looking," said John Lepinski, a poll watcher and former Democratic Party chairman for Outagamie County.
He said that as a result of the scrutiny, the line to register moved slowly. Finally, he said, some students gave up and left.
Ms. Engelbrecht said the True the Vote observer at Lawrence University believed that students were being permitted to register and vote without proper identification.
In Racine, conservative poll watchers also alleged fraud, including a claim that a busload of union members from Michigan had come to Wisconsin to vote illegally. The Racine County Sheriff's Department determined that the accusation had been based on an anonymous call to a radio station.
"There is no evidence this bus convoy existed or ever arrived in Racine County," the Sheriff's Office said.
As for the buses her organization saw in Wisconsin, Ms. Engelbrecht could not provide details. "It was reported to us that this had occurred," she said. "I know these sightings were also being reported on the radio."
The Code Red Cavalry
Driving down the Interstate in Florida, you may see an R.V. wrapped with a picture of Abraham Lincoln.
These eye-catching vehicles are mobile command centers for registering and energizing voters. They are part of a citizen effort to "defeat Obama, hold the House and win the Senate in November," Fred Solomon, a retired Alabama businessman, said in an e-mail to fellow Tea Party supporters.
Mr. Solomon is a coordinator for Code Red USA, the plan to flood swing states with conservative volunteers. "Partnering with True the Vote, a nonprofit, nonpartisan watchdog group, we will train and put election observers in polling places in the swing states to reduce voter fraud," Mr. Solomon said in his e-mail.
Code Red USA is financed by the Madison Project, a political action committee whose chairman is former Representative Jim Ryun, a Kansas Republican who was regarded as among the most conservative members of Congress. The provocative video promoting Code Red accuses Democrats of "a clear intent to commit massive voter fraud."
Despite Mr. Solomon's e-mail and the video, which identifies True the Vote as a participant, Ms. Engelbrecht said her group has no role in the effort.
Nevertheless, Mr. Solomon and many other conservative activists have followed Ms. Engelbrecht's lead.
Mr. Solomon said he was a volunteer poll watcher in Wisconsin and is concerned that voter fraud is rampant around the country. "We just don't understand why dead people are voting," he said.
Finding that someone voted in the name of a dead person is the holy grail of the voter integrity movement, said Jay DeLancy, a retired Air Force officer in North Carolina who embraced the cause after attending a True the Vote meeting last year. Mr. DeLancy, who runs the Voter Integrity Project of North Carolina, said the group recently submitted the names of 30,000 people who he said were dead yet remained on voter rolls in the state.
Earlier this year, he challenged more than 500 registered voters who he said were not American citizens. After reviewing the challenges, election officials refuted most of them, but confirmed that three were noncitizens who had registered improperly. One had voted.
Mr. DeLancy said he was convinced that the elections agency overlooked many noncitizen voters.
"They want me to look stupid and to look like I'm wasting taxpayer money," Mr. DeLancy said.
He said he split from True the Vote partly because the group raised concerns about focusing on immigrants. "They're not wanting to be branded some kind of anti-immigrant activist group," Mr. DeLancy said.
Mr. DeLancy said he made challenges after comparing voting rolls with citizenship information in jury duty records.
The strategy was used by Mr. O'Keefe, who is known for undercover video stings. Shortly after the North Carolina primary in May, Mr. O'Keefe posted a video aimed at proving noncitizens were registered to vote.
A narrator says: "William Romero is registered to vote in North Carolina. Here is a copy of his voter registration form, where it says he was born in Colombia, South America. He is not, however, a United States citizen."
The video cuts to a young man, dressed in green lederhosen, walking into Mr. Romero's polling place and giving Mr. Romero's name and address. When he is asked to sign his name certifying that he is William Romero, the man, whose right hand was bandaged, says he is unable to sign and leaves.
The video later shows what appears to be the same man in green lederhosen impersonating a registered voter named Zbigniew Gorzkowski.
Not only were Mr. Romero and Mr. Gorzkowski citizens, but the State Board of Elections concluded that Mr. O'Keefe's operatives may have broken several laws, and turned over evidence to prosecutors. "Further, the videos made false or unfounded allegations that only hurt the elections process," North Carolina election officials said in a report.
Mr. O'Keefe, who did not respond to requests for an interview, is on probation for unlawfully entering a federal building in New Orleans in an aborted sting targeting Senator Mary L. Landrieu, Democrat of Louisiana.
Mr. Romero could not be reached for comment. Mr. Gorzkowski, a naturalized United States citizen who operates a deli in North Carolina, said the video was extremely embarrassing, especially after a Polish newspaper ran an article suggesting that he was at the center of a voting scandal in the United States.
'Never Had Any Problem'
Late last month, Ms. Engelbrecht was in Columbus, Ohio, for a True the Vote workshop. About 90 people signed up for the event at a suburban Holiday Inn, where they listened to speeches and discussed how to challenge questionable voters, including 51,000 "nonexistent" people in just one county that True the Vote's Ohio volunteers say are registered to vote.
During the meeting, Anita MonCrief, True the Vote's senior adviser, unleashed her vitriol at what she said was a coalition of voter registration groups, accusing them of "doing voter fraud since at least the early '90s," she said.
"And these groups target minority areas. Why? Because it's so much easier to go work in those areas where they say people have been forgotten or they don't have a voice. Then, when anybody pays a little bit of attention to the fact that there's a high level of fraud coming out of the African-American communities, they say: 'Oh, you're a racist. You don't want black people to vote,' " said Ms. MonCrief, who is black. "Vote fraud deniers is what I call them."
After the event, the volunteers, known as the Ohio Voter Integrity Project, submitted challenges of 380 registered voters in Hamilton County, which includes Cincinnati. One of the voters, Teresa Sharp, received a notice from her local Board of Elections stating that her family's right to vote had been challenged and ordering her to attend a hearing on Sept. 10.
"I've always voted," said Ms. Sharp, who had even been a poll worker. "Never had any problem."
At the hearing, she said she asked, "Why are you all harassing me?" She said she believed it was because "either they don't want Obama in there or the fact that I'm black."
Amy Searcy, the director of the Hamilton County Board of Elections, said there was no discernible racial pattern in the challenges. Of the 380 challenges, about 35 voters will have to prove that their addresses are current if they appear at the polls. A vast majority of the objections were thrown out.
In the case of Ms. Sharp, a representative of the Ohio Voter Integrity Project withdrew the challenge and apologized to the family.
This article originally appeared in The New York Times.