DENVER, the UNITED STATES, Nov. 1 -- With a week to go before the highly contentious 2016 U.S. presidential election, voter fraud emerged as a controversial theme, which was mentioned by Republican candidate Donald Trump frequently and used as a consistent weapon against his Democratic counterpart Hillary Clinton.

On the campaign trail, Trump regularly quoted a 2012 study by the Pew Center on the States, saying that 24 million registrations were outdated or invalid, 2 million registrants were dead, and 2.75 million were registered in more than one state.

He fueled the voter fraud debate again last week in Golden, Colorado when he asserted that elections officials who count ballots, "will say, 'Oh, here's a ballot, bing, here's another ballot, throw it away, throw. Oh, here's one I like, we'll keep that one.' I have real problems..."

For these two areas of possible fraud spoken by Trump -- mail in votes that were individually handled and counted by elections officials, and cases of identity fraud where individuals would vote more than once using falsified identifications, election experts believed that the pugnacious billionaire intentionally overstated problems and it was a campaign tactic.

"By raising doubts about the integrity of the voting system, Trump is making it easier to explain what happened if he loses, and is sowing seed of doubt about the legitimacy of Hillary Clinton's presidency," Barry Burden, professor of political science at the University of Wisconsin, told Xinhua Tuesday.

Burden, considered one of the foremost experts on the American voting system and election fraud, conducted extensive research and authored more than 100 articles on the issue in the past decade.

"Voter fraud is extremely rare and not widespread," Burden asserted, "Although the U.S. election system is far from perfect, in no sense are American elections 'rigge' in the ways Trump is suggesting."

He also told Xinhua that fortunately states such as Colorado had impressive systems in place to track mailed ballots throughout the process.

Last week, an investigative report by Denver's CBS4 TV uncovered a dozen cases where Coloradans were suspected of voting twice.

The study cited Lincoln Wilson, a registered Republican from Hale, Colorado, for voting in both Colorado and Kansas in 2010, 2012 and again in 2014, and Hale admitted he had double-voted.

Kansas also charged James Criswell and Sharon Farris, both Colorado Republicans, with double voting. Their cases were still pending.

Kansas Secretary of State Kris Kobach said he believes there were up to 10,000 people double registered in Colorado and Kansas. He publicly warned them, "Don't do it...we'll catch you."

Other instances emerged in the study whereby ballots were cast in the names of Coloradans who were dead, yet someone else cast a vote in their name.

Trump campaign officials also pointed to a 2014 report in the political journal Electoral Studies that figured out U.S. election registration procedures were flawed and as many as one in 15 non-United States citizens living in the country could have cast illegal ballots in the 2008 election.

Like Pew surveys cited by Trump often, the Electoral Studies also drawn fire and criticism from academic sources, who insisted that both represented a great minority of research supporting American voter fraud claims.

The oft-repeated assertion from the Trump campaign was that Democrats steal elections via fraud, however, the first such case of election fraud prosecuted in 2016 was last week when an Iowa Trump supporter was arrested and charged for attempting to vote twice in the upcoming election.

Terri Lynn Rote, 55, was charged with first-degree election misconduct and faced a 5-year prison sentence if convicted. She told the media her reason for breaking the law was that she thought the election was "rigged" and that her vote might go to "Hillary Clinton."

"Of the many types of fraud that might exist, voter impersonation at the polls is the least common and easiest to detect," Burden said, who pointed to a study suggesting that voter fraud was just a tiny part of the American election landscape.

A study investigating claims of voter fraud between 2000 to 2014 by Los Angeles' Loyola Law School uncovered only 31 credible claims of voter impersonation out of 1 billion ballots that were cast.

A 2012 Arizona State University journalism project analyzed 2,068 allegations of election fraud between 2000 and 2012 and said only 10 had involved misrepresentation.

And a Missouri study, after the 2000 presidential elections, concluded that only six of the 2,361,586 Missouri votes cast were found to have been ineligible.

However, not all voters trusted the research results. Many Democratic supporters still kept in mind that 2000 presidential candidate Al Gore was robbed of the presidency by widespread voting fraud in Florida, a case that eventually went to the U.S. Supreme Court, dominated by Republicans, who awarded the presidential election to George W. Bush.

Gore won the 2000 popular vote, 50,999,897 to 50,456,002, but due the American 'Electoral College' system, Bush was able to claim victory based solely on the Florida outcome, which was widely suspected to be fraudulent.

The Florida controversy triggered widespread voting reform, as many individual states took the initiative to review their voting systems and replace outdated lever and punch card voting machines.

The U.S. Congress also addressed the problem, passing the "Help America Vote Act" of 2002 that established basic guidelines for voting machines used in federal elections, and provided federal funds to states to replace outdated voting machines and to meet the new federal requirements.

But the new voting machines raise new concerns this year as more than 125,000 signed a petition posted Oct. 21, on the White House website that said, "We the people ask Congress to meet in emergency session about removing George Soros-owned voting machines from 16 states."

With recent WikiLeaks emails showing that Clinton received foreign policy directives and coordinated on domestic policy with Soros, along with receiving tens of millions of dollars from the billionaire, it's clear some Americans suspected that these shadowy players may pull the strings behind the curtains of the upcoming presidential election.