ATLANTA (AP) — An Associated Press review of every potential case of voter fraud in the six battleground states disputed by former President Donald Trump has found fewer than 475 — a number that would have made no difference in the 2020 presidential election.

Democrat Joe Biden won Arizona, Georgia, Michigan, Nevada, Pennsylvania and Wisconsin and their 79 Electoral College votes by a combined 311,257 votes out of 25.5 million ballots cast for president. The disputed ballots represent just 0.15% of his victory margin in those states.

The cases could not throw the outcome into question even if all the potentially fraudulent votes were for Biden, which they were not, and even if those ballots were actually counted, which in most cases they were not.

The review also showed no collusion intended to rig the voting. Virtually every case was based on an individual acting alone to cast additional ballots.

The findings build on a mountain of other evidence that the election wasn’t rigged, including verification of the results by Republican governors.

The AP review, a process that took months and encompassed more than 300 local election offices, is one the most comprehensive examinations of suspected voter fraud in last year’s presidential election. It relies on information collected at the local level, where officials must reconcile their ballots and account for discrepancies, and includes a handful of separate cases cited by secretaries of state and state attorneys general.

Contacted for comment, Trump repeated a litany of unfounded claims of fraud he had made previously, but offered no new evidence that specifically contradicted the AP’s reporting. He said a soon-to-come report from a source he would not disclose would support his case, and insisted increased mail voting alone had opened the door to cheating that involved “hundreds of thousands of votes.”

“I just don’t think you should make a fool out of yourself by saying 400 votes,” he said.

These are some of the culprits in the “massive election fraud” Trump falsely says deprived him of a second term:

A Wisconsin man who mistakenly thought he could vote while on parole.

A woman in Arizona suspected of sending in a ballot for her dead mother.

A Pennsylvania man who went twice to the polls, voting once on his own behalf and once for his son.

The cases were isolated. There was no widespread, coordinated deceit.

The cases also underscore that suspected fraud is both generally detected and exceptionally rare.

“Voter fraud is virtually non-existent,” said George Christenson, election clerk for Milwaukee County in Wisconsin, where five people statewide have been charged with fraud out of nearly 3.3 million ballots cast for president. “I would have to venture a guess that’s about the same odds as getting hit by lightning.”

Even in the state with the highest number of potential fraud cases — Arizona, with 198 — they comprised less than 2% of the margin by which Biden won.

Trump has continued to insist that the election was fraudulent by citing a wide range of complaints, many of them involving the expansion of mail voting because of the pandemic. As the Republican weighs another run for president in 2024, he has waded into some GOP primary contests, bestowing endorsements on those who mimic his “Stop the steal” rhetoric and seeking to exact revenge on some who have opposed his efforts to overturn the results.

Trump’s false claims of a stolen election fueled the deadly Jan. 6 attempted insurrection at the Capitol, have led to death threats against election officials and have become deeply ingrained within the GOP, with two-thirds of Republicans believing Biden’s election is illegitimate. Republican lawmakers in several states have used the false claims as justification to conduct costly and time-consuming partisan election reviews, done at Trump’s urging, and add new restrictions for voting.

The number of cases identified so far by local elections officials and forwarded to prosecutors, local law enforcement or secretaries of state for further review undercuts Trump’s claim. Election officials also say that in most cases, the additional ballots were never counted because workers did their jobs and pulled them for inspection before they were added to the tally.

“There is a very specific reason why we don’t see many instances of fraud, and that is because the system is designed to catch it, to flag it and then hold those people accountable,” said Amber McReynolds, a former director of elections in Denver and the founding CEO of the National Vote at Home Institute, which promotes mail voting.

The AP’s review of cases in the six battleground states found no evidence to support Trump’s various claims, which have included unsupported allegations that more votes were tallied than there are registered voters and that thousands of mail-in ballots were cast by people who are not on voter rolls. Dozens of state and federal courts have rejected the claims.

White House spokesman Andrew Bates said the AP's reporting offered further proof that the election was fairly conducted and decided, contrary to Trump's claims.

“Each time this dangerous but weak and fear-ridden conspiracy theory has been put forward, it has only cemented the truth more by being completely debunked — including at the hands of elections authorities from both parties across the nation, nonpartisan experts, and over 80 federal judges,” he said.

Experts say to pull off stealing a presidential election would require large numbers of people willing to risk prosecution, prison time and fines working in concert with election officials from both parties who are willing to look the other way. And everyone somehow would keep quiet about the whole affair.

“It would be the most extensive conspiracy in the history of planet Earth,” said David Becker, a senior trial attorney in the Justice Department’s Civil Rights Division during the presidencies of Bill Clinton and George W. Bush who now directs the nonprofit Center for Election Innovation & Research.

Separate from the fraud allegations are claims by Trump and his allies that voting systems or ballot tallies were somehow manipulated to steal the election. Judges across the country, of both parties, dismissed those claims. That includes a federal judge in Michigan who ordered sanctions against attorneys allied with Trump for intending to create “confusion, commotion and chaos” in filing a lawsuit about the vote-counting process without checking for evidence to support the claims.

Even Trump’s former attorney general, William Barr, said a month after the election that there was no indication of widespread fraud that could change the result.

For its review, AP reporters in five states contacted roughly 340 election offices for details about every instance of potential voter fraud that was identified as part of their post-election review and certification process.

After an election is over, officials research voter records, request and review additional information if needed from the state or other counties, and eventually decide whether to refer potential fraud cases for further investigation — a process that can take months.

For Wisconsin, the AP relied on a report about fraud investigations compiled by the state and filed public records requests to get the details of each case, in addition to prosecutions that were not initially reported to the state elections commission. Wisconsin is the only one of the six states with a centralized accounting of all potential voter fraud cases.

A state-by-state accounting:

—ARIZONA: Authorities have been investigating 198 possible fraud cases out of nearly 3.4 million votes cast, representing 1.9% of Biden’s margin of victory in the state. Virtually all the cases were in Pima County, home to Tucson, and involved allegations of double voting. The county has a practice of referring every effort to cast a second ballot to prosecutors, something other offices don’t do. In the Pima cases, only one ballot for each voter was counted. So far, nine people have been charged in the state with voting fraud crimes following the 2020 election. Six of those were filed by the state attorney general’s office, which has an election integrity unit that is reviewing an undisclosed number of additional cases.

—GEORGIA: Election officials in 124 of the state’s 159 counties reported no suspicious activity after conducting their post-election checks. Officials in 24 counties identified 64 potential voter fraud cases, representing 0.54% of Biden’s margin of victory in Georgia. Of those, 31 were determined to be the result of an administrative error or some other mistake. Eleven counties, most of them rural, either declined to say or did not respond. The state attorney general's office is reviewing about 20 cases referred so far by the state election board related to all elections in 2020, including the primary, but it was not known if any of those overlapped with cases already identified by local election officials.

—MICHIGAN: Officials have identified 56 potential instances of voter fraud in five counties, representing 0.04% of Biden’s margin of victory in the state. Most of the cases involved two people suspected of submitting about 50 fraudulent requests for absentee ballots in Macomb, Wayne and Oakland counties. All the suspicious applications were flagged by election officials and no ballots were cast improperly.

—NEVADA: Local officials identified between 93 and 98 potential fraud cases out of 1.4 million ballots cast, representing less than one-third of 1% of Biden’s margin of victory. More than half the total — 58 — were in Washoe County, which includes Reno, and the vast majority involved allegations of possible double voting. The statewide total does not include thousands of fraud allegations submitted to the state by local Republicans. Republican Secretary of State Barbara Cegavske has said many of those were based “largely upon an incomplete assessment of voter registration records and lack of information concerning the processes by which these records are compiled and maintained.” It’s not known how many remain under investigation.

—PENNSYLVANIA: Election officials in 11 of the state’s 67 counties identified 26 possible cases of voter fraud, representing 0.03% of Biden’s margin of victory. The elections office in Philadelphia refused to discuss potential cases with the AP, but the prosecutor’s office in Philadelphia said it has not received any fraud-related referrals.

—WISCONSIN: Election officials have referred 31 cases of potential fraud to prosecutors in 12 of the state’s 72 counties, representing about 0.15% of Biden’s margin of victory. After reviewing them, prosecutors declined to bring charges in 26 of those cases. Meagan Wolfe, administrator of the Wisconsin Elections Commission, said the number of cases in 2020 was “fairly run of the mill.”

AP’s review found the potential cases of fraud ran the gamut: Some were attributed to administrative error or voter confusion while others were being examined as intentional attempts to commit fraud. In those cases, many involved people who sought to vote twice — by casting both an absentee and an in-person ballots — or those who cast a ballot for a dead relative such as the woman in Maricopa County, Arizona. Authorities there say she signed her mother’s name on a ballot envelope. The woman’s mother had died a month before the election.

The cases are bipartisan. Some of those charged with fraud are registered Republicans or told investigators they were supporters of Trump.

Donald Holz is among the five people in Wisconsin who face voter fraud charges. He said all he wanted to do was vote for Trump. But because he was still on parole after being convicted of felony drunken driving, the 63-year-old retiree was not eligible to do so. Wisconsin is not among the states that have loosened felon voting laws in recent years.

Holz said he had no intention to break the law and only did so after he asked poll workers if it was OK.

“The only thing that helps me out is that I know what I did and I did it with good intentions,” Holz said after an initial court appearance in Fond du Lac. “The guy upstairs knows what I did. I didn’t have any intention to commit election fraud.”

In southeast Pennsylvania, 72-year-old Ralph Thurman, a registered Republican, was sentenced to three years’ probation after pleading guilty to one count of repeat voting. Authorities said Thurman, after voting at his polling place, returned about an hour later wearing sunglasses and cast a ballot in his son’s name.

After being recognized and confronted, Thurman fled the building, officials said. Thurman’s attorney told the AP the incident was the result of miscommunication at the polling place.

Las Vegas businessman Donald “Kirk” Hartle was among those in Nevada who raised the cry against election fraud. Early on, Hartle insisted someone had unlawfully cast a ballot in the name of his dead wife, and state Republicans seized on his story to support their claims of widespread fraud in the state. It turned out that someone had cast the ballot illegally — Hartle, himself. He agreed to plead guilty to a reduced charge of voting more than once in the same election.

Hartle’s attorney said the businessman, who is an executive at a company that hosted a Trump rally before the election, had accepted responsibility for his actions.

Additional fraud cases could still surface in the weeks and months ahead. One avenue for those is the Electronic Registration Information Center, a data-sharing effort among 31 states aimed at improving state voter rolls. The effort also provides states with reports after each general election with information about voters who might have cast ballots in more than one state.

In the past, those lists have generated small numbers of fraud cases. In 2018, for example, Wisconsin used the report to identify 43 additional instances of potential fraud out of 2.6 million ballots cast.

Official post-election audits and other research have shown voter fraud to be exceptionally rare. A nonpartisan audit of Wisconsin’s 2020 presidential election found no evidence of widespread fraud and a Republican lawmaker concluded it showed that elections in the state were “safe and secure,” while also recommending dozens of changes to how elections are run. In Michigan, Republican state senators issued a report earlier this year saying they had found “no evidence of widespread or systematic fraud” in the 2020 election.

Not only do election officials look for fraud, they have procedures to detect and prevent it.

For mail voting, which expanded greatly last year because of the pandemic, election officials log every mail ballot so voters cannot request more than one. Those ballots also are logged when they are returned, checked against registration and, in many cases, voter signatures on file to ensure the voter assigned to the ballot is the one who cast it.

If everything doesn’t match, the ballot isn’t counted.

“Often, we don’t get to fraud,” said Jennifer Morrell, a former local election official in Utah and Colorado who advises election officials on security and other issues. “Say we have evidence that something might not be correct, we ask the voter to provide additional documentation. If the person doesn’t respond, the ballot isn’t accepted. The fraud never happened.”

If a person who requested a mail ballot shows up at a polling place, this will become apparent when they check in. Typically, poll workers either cancel the ballot that was previously issued, ensuring it’s never counted, or ask the voter to complete a provisional ballot that will only be counted if the mail ballot is not.

In Union County, Georgia, someone voted in person and then election officials found their ballot in a drop box. Since the person had already voted, the ballot in the drop box was not counted and the case was referred to the state for investigation, Deputy Registrar Diana Nichols said.

“We can tell pretty quick whenever we pull up that record -- wait a minute, this person has already voted,” Nichols said. “I’m not saying it’s foolproof. We are all human, and we all make mistakes. But as far as the system is set up, if you follow the rules and the guidelines set up by the state, I think it’s a very good system.”

The final step is the canvassing process in which election officials must reconcile all their counts, ensuring the number of ballots cast equals the number of voters who voted. Any discrepancies are researched, and election officials provide detailed explanations before the election can be certified.

Often, an administrative error can raise questions that suggest the potential for fraud.

In Forsyth County, Georgia, election officials were asked by Arizona investigators for records confirming that a voter had also cast a ballot in Georgia last November. It turns out that voter didn’t cast a ballot but was listed as having done so because their registration number was mistakenly associated with another voter’s record in the county’s system, according to a letter sent by county election officials.

In other cases, it could be as simple as a voter signing on the wrong line next to another person’s name in a paper pollbook at their polling place. Once researched, it quickly becomes clear no fraud occurred.

Republican lawmakers have argued there are security gaps in the process, using concerns of fraud to justify restrictions on voting laws. This has happened even in places where Republican lawmakers have pushed back against Trump’s false claims and said the 2020 election was valid.

The review by Republican lawmakers in Michigan that found no systemic fraud cited various claims they had investigated. For example, senators were provided with a list of over 200 voters in Wayne County who were believed to be dead. Of these, the report noted, only two instances involved actual dead voters. The first was due to a clerical error in which a son had been confused with his dead father and the second involved a 92-year-old woman who had died four days before the election.

And yet, Republicans in the state are collecting signatures for a citizen initiative that would allow the GOP-controlled legislature to approve voting restrictions and bypass a veto by the Democratic governor. Republicans say mail voting needs to be more secure as more people embrace it.

“These bills will restore confidence in our elections,” said GOP Rep. Ann Bollin, chairwoman of the Michigan House Elections and Ethics Committee and a former township clerk. “Voters want to know their vote will count and that they, and only they, are casting their own ballot.”

Overall, 80% of counties in the six states reviewed by the AP reported no suspicious activity after completing their post-election reviews. This was true of both small and large counties, something experts said was to be expected given how rare voter fraud has been.

Limited instances of fraud do occur, as the AP review illustrates, but safeguards ensure they are few and that they are caught, said Ben Hovland, a Democrat appointed by Trump to serve on the U.S. Election Assistance Commission, which supports the state and local officials who administer elections.

“Every credible examination has shown there was no widespread fraud” in the 2020 presidential election, Hovland said. “Time and again when we have heard these claims and heard these allegations, and when you do a real investigation, you see that it is the exception and not the rule.”

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Contributing to this report were Associated Press data journalist Camille Fassett in Oakland, California; reporter Colleen Long in Washington; AP state government reporters Scott Bauer in Fond du Lac, Wisconsin; Bob Christie in Phoenix; David Eggert in Lansing, Michigan; Anthony Izaguirre in Tallahassee, Florida; and Michelle L. Price in New York City; and other AP reporters in Michigan and Pennsylvania.