Ballots envelopes sit in a bin inside a polling center at the Boulder County Clerk and Recorder's office on Election Day 2014. 

(Photo: AP/Brennan Linsley)

Throughout his campaign, but especially lately, Republican presidential nominee Donald Trump has insisted without proof that there will be widespread voter fraud on Election Day. He’s been encouraging his followers to get out and watch polling places.

“Go to your place and vote, and then go pick some other place, and go sit there with your friends and make sure it's on the up and up,” Trump said in Detroit in late September.

Then earlier in October Trump tweeted, “Of course there is large scale voter fraud happening on and before election day. Why do Republican leaders deny what is going on? So naive!” On his website, a form asks volunteers to help “stop Crooked Hillary from rigging this election.”

At first blush, a campaign recruiting volunteers to monitor polling places is perfectly normal. Partisan poll watchers, recruited by political parties, issue committees and unaffiliated and write-in candidates, are part of why the country’s electoral system works as well as it does. They are trained by either counties or parties under rules from the secretary of state’s office.

But election analysts around the country worry Trump’s call to monitor polling places will draw out untrained volunteers who might cause trouble -- particularly in areas with many minority voters. Indeed, one Trump supporter told the Boston Globe he would target Mexicans, Syrians and “people who can’t speak American.”

“It’s very common to have people at the polls,” Rick Hasen, an election law expert and professor at the University of California at Irvine’s School of Law, told the Washington Post. “What’s different is that he is couching it in an incendiary way by saying ‘crooked Hillary’ wants to steal the election. That seems to be an invitation to go and make trouble.”

The opportunity for trouble is diminished in Colorado because most ballots are cast by mail. In 2014, 95 percent of votes cast were mail-in ballots either returned by post or at a drop-off location. That means many fewer people waiting in line at polling places on Election Day, where voter intimidation is most likely to happen.

Mail-in ballots may limit opportunities for voter intimidation, said Martha Tierney, legal counsel for the Colorado Democratic Party. But she warned that it can still happen on social media and other avenues.

"Things like mailers that say 'Republicans vote on Tuesday, Democrats vote on Wednesday," she said. “It's the kind of misinformation that can lead to intimidation. Historically Colorado has not seen a lot of that. But we’ve seen it around the country."

Denver election officials say even if most people won’t come inside a polling place, they still take the issue of voter intimidation seriously and will be prepared to deal with any untrained poll watchers. The only people allowed in or within 100 feet of a Colorado polling place are voters, election judges and officials, poll watchers, media observers and federal officials.

“If it's someone outside of that, they are not going to be allowed to sort of hang around in the voting space,” said Amber McReynolds, director of elections for Denver.

Asked whether extra security would be stationed in precincts with more minority voters, McReynolds said every polling place will have the same standard. And for the first time this year, Denver’s election judges will be trained for active shooter situations. McReynolds said that’s in response to the rise in mass shootings across the county, not to any campaign rhetoric.

Republican Secretary of State Wayne Williams said anyone is welcome to observe the voting process. But there’s a line that should not be crossed, he said.

“What they can't do is impede anyone from voting. They can't intimidate anyone from lawfully voting,” Williams said.

Under state law, interfering with or intimidating a voter is a misdemeanor punishable by up to a year in jail and up to a $1,000 fine.

Scott Gessler, the former Republican secretary of state who currently handles legal operations for Trump’s campaign in Colorado, said concerns about untrained poll workers are overblown.

"If there's examples of harassment, I think that needs to be dealt with sternly. But I've rarely, if ever, seen that happen,” Gessler said.

Gessler is more worried about flaws in the state’s voter database that lead to voters erroneously receiving more than one ballot in the mail. Fox31 recently found a Colorado woman who received two ballots -- one addressed to Makinzy Kay Olson and another to Makinzy Olson. The Gazette in Colorado Springs reported on a similar case in 2012.

But exactly how often such mistakes happen isn’t clear.

"We don't know the numbers because the statute doesn't allow state election officials to really clean the voter rolls properly,” Gessler said. Despite that, Gessler said he has confidence in the system here.

"Absent that … I've not seen any evidence in Colorado that rises to the level of concerns that you've seen historically in other cities,” he said.

Gessler initially didn’t back Trump. He was a supporter of Texas Sen. Ted Cruz and called Trump’s Colorado campaign a “hot mess” at the Republican National Convention in Cleveland this summer. He said he now supports Trump because Trump became the party’s nominee.

Gessler described the campaign’s efforts to recruit official poll watchers as “generally pretty good.” He said they had some problems finding Republican volunteers in Boulder, he said, but he thinks the campaign will be able to have watchers in the “critical” parts of the heavily Democratic county.

The state Republican Party says there’s been no drop off in interest or difficulty recruiting poll watchers and election judges compared to prior years.

“We feel very good about where we are in terms of recruiting folks and making sure all of those positions are filled,” party spokesman Kyle Kohli said via email.

Democrats also say they’ll have credentialed watchers at most polling places across the state.

“In some of the more rural counties, it’s just hard to get people,” said Tierney, who also runs the Democrats’ poll watching program.

And if you’re looking to get involved, there’s still time to be a volunteer poll watcher. Contact your party’s local or state office, the issue committee for a ballot measure you support or oppose, or the unaffiliated or write-in candidate of your choice.

CPR News’ Mike Lamp contributed to this report.