Indeed, state election officials have expressed confidence in the system and said the opportunity for widespread fraud was low. And experts and Trump's hand-picked FBI director said there was no evidence of widespread fraud.
David Schultz, a national expert on election law, and professor at Hamline University, told ABC News that despite the significantly higher number of Americans voting by mail this year, he does not believe that the increase will lead to a measurable uptick of voter fraud.
“What Trump is setting up here is something incredibly dangerous, in terms of questioning the legitimacy of the elections,” stated Schultz.
Schultz said the president is “calling into question the legitimacy of the election, should he lose come November, because he can then say, ‘Well, I didn't really legitimately lose... it was because of voter fraud."
The president began talking about alleged incidents of mail-in ballot fraud at the end of this summer.
He has often made a distinction, which others have rejected, between states that mail unsolicited ballots to voters and those that require residents to request absentee ballots.
“The ballots are out of control,” the president said of mail-in ballots at a White House briefing on Sept. 23.
“We want to make sure the election is honest, and I’m not sure that it can be,” he said in another briefing the next day. “I don’t know that it can be with this whole situation — unsolicited ballots. They’re unsolicited; millions being sent to everybody. And we’ll see.”
Here are some alleged examples cited by Trump and his surrogates and what we know about them:
Ballots in Pennsylvania
During the first presidential debate, Trump cited an incident in Pennsylvania, in which he said ballots from his supporters were discovered in the garbage.
“They found ballots in a wastepaper basket three days ago and they all had the name -- military ballots, they were military,” he said. “They all had the name Trump on them."
But state officials had looked into the incident and suggested it was different from the way Trump framed it. Seven of the ballots had Trump's name on them and two remained unopened.
Pennsylvania's secretary of state, Kathy Boockvar, said it amounted to a mistake and not "intentional fraud." Boockvar, a Democrat, blamed the blunder on a temporary independent contractor who was assigned to sort mail at the election bureau in Luzerne County and who accidentally tossed nine military ballots in the trash.
The error was discovered by officials two days later and remedied.
West Virginia and Wisconsin claims
Trump also falsely claimed, during the debate, that mail-in ballots were being “sold,” by mail carriers in West Virginia, and others were being "dumped in rivers.”
West Virginia’s Republican secretary of state, Mac Warner, refuted the president’s allegation, saying a postal worker pleaded guilty in July to altering eight absentee ballot applications -- not the ballots themselves – ahead of the state’s primary election earlier this year. No money was exchanged. A county clerk discovered the problem and reported it to the secretary of state.
“The system worked, and we were able to rapidly assure the voters of West Virginia that the election was secure,” Warner said.
Additionally, in the days prior to the debate, an incident involving ballots in Wisconsin went viral in conservative circles online, after several conservative news outlets posted the story, which then circulated to thousands of recipients on social media.
The incident described by Trump pertained to an ongoing investigation in Wisconsin. However, no ballots were thrown in a river.
Discarded mail was found in a ditch, in Greenville, Wisconsin, which was supposed to be in transit to the post office. Among the lost mail were “several” absentee ballots, but none were Wisconsin ballots, according to the Wisconsin Elections Commission. And the state said that had they been Wisconsin ballots, safeguards would have been in place to identify any issues.
White House press secretary Kayleigh McEnany was repeatedly pressed by reporters to clarify where the "river" that Trump talked about was located, but she declined to answer.
Florida ballot requests
Last week, President Trump retweeted an article about a man in Manatee County, Florida who allegedly tried to obtain a mail-in ballot for his dead wife by forging her signature on the ballot request. The county elections office caught this incident after checking the voter rolls and notified local law enforcement, who arrested the man and charged him with a third-degree felony voter charge.
An election supervisor told ABC News that the incident was incredibly rare, and was the first instance of voter fraud he's seen in the county of nearly 400,000in the eight years on the job.
According to local reports, the man is a Trump supporter who said he “wanted to test the system.” However, the story played out differently on social media, where right wing sites pushed emphasized that the man, Larry Wiggins, who is Black,was a registered Democrat.
As of Oct. 15, nine of the Top 10 most shared posts on Facebook about the case were made by right-wing accounts or posted by conservative outlets.
Attorney General Barr’s Texas allegations
Trump's attorney general, William Barr, has made similarly inaccurate allegations of the potential for mail-in voter fraud.
“Elections that have been held with mail have found substantial fraud and coercion,” Barr said in an interview on CNN on Sept. 2. The attorney general cited a 2017 case in Texas, saying: “we indicted someone in Texas” who Barr alleged had collected 1,700 ballots and “made them out and voted for the person he wanted to.”
"That kind of thing happens with mail-in ballots and everyone knows that," Barr added.
However, Barr’s depiction of the case was inaccurate --no such federal case was brought. And Andy Chatham, a former assistant district attorney, and democrat, who worked on the suspected mail-in voter fraud in Dallas County investigation in 2017, told ABC News that "this wasn't a case of voter fraud. This was a case of what we think was a political consultant trying to scam candidates."
Nearly 700 ballots — not 1,700 — were investigated for possible fraud, because they were all linked to the same person, who had helped voters fill out the ballots.
Individual voters were contacted and the ballots were not only split between candidates, but generally viewed as accurately reflecting their choices. "The statistical percentage of ballots that were returned were almost exactly what the election result was," Chatham said.
Voter fraud is rare in the United States
Fear about the integrity of the election seems to resonate with some of Trump’s partisans, despite a complete lack of evidence indicating that there is a problem.
A recent poll from Pew Research Center found that 43% of Republicans and Republican-leaning independents believed that voter fraud has been a major problem when it comes to mail-in voting for presidential elections. Among Democrats and Democratic-leaning independents, only 11% believed it's been a major problem.
Election officials in Democrat and Republican states alike have been clear that they have confidence in their election process, and experts agree that the risk of fraud is very low.
Nicholas Stephanopoulos, an expert on election law and constitutional law and a professor at Harvard Law School, said “all available evidence indicates that mail-in voting in the United States is safe and secure. In states that use mail-in voting, there are infinitesimal rates of problems. More importantly, in these states, there are more people who vote; turnout is higher and so democracy is more robust.”
The number of cases of proven voter fraud is indeed infinitesimal, concurs Schultz, citing an extensive study of American election fraud, conducted at Arizona State University, which revealed that the rate is minuscule; there were only 10 cases of proven voter fraud, out of every 150 million eligible voters – and thus, “the odds are not too far from your odds of winning a Powerball ticket,” said Schultz.
When mistakes are found, said Schultz, they tend to be clerical errors by election officials, confusion about a voter’s eligibility to vote, such as with ex-felons, or a mistake made by a voter.
However, even when these mistakes are added up, the rate of voter fraud is very rare, and therefore, “there is absolutely no evidence that shows that voter fraud is so widespread that it has changed the outcome of any election in the United States,” Schultz said.
There are states across the country that have been voting almost exclusively by mail for years, such as Washington state, he said, and “we have never seen an uptick in fraud as a result, so we've got some natural experiments out there.”
Although there may be a few more instances of fraud, given the large number of Americans voting by mail, “the percentage [of fraud] is still going to be the same -- which is infinitesimally small.”
In several states across the country, including Montana, Ohio, New Jersey, Nevada, Louisiana Pennsylvania, Illinois, judges have dismissed allegations of potential voter fraud made by the Trump campaign. President Trump himself requested a mail ballot for Florida’s Republican primary in March, and has voted absentee in past cycles.
FBI Director Christopher Wray, who Trump appointed, also refuted Trump’s claim of widespread voter fraud during a Senate hearing in September.
“Now, we have not seen, historically, any kind of coordinated national voter fraud effort in a major election, whether it’s by mail or otherwise,” he said. “We have seen voter fraud at the local level from time to time.