Warning darkly of a stolen election, Donald J. Trump has called on supporters to turn out in droves on Election Day to monitor polling places, telling them they need to be vigilant against widespread voter fraud and a rigged outcome.
“Voter fraud is all too common, and then they criticize us for saying that,” he said at a rally Tuesday in Colorado Springs. “But take a look at Philadelphia, what’s been going on, take a look at Chicago, take a look at St. Louis. Take a look at some of these cities, where you see things happening that are horrendous.”
His language has stirred increasing fears of intimidation of minorities inside polling places, where their qualifications to vote could be challenged, or outside, where they would face illegal electioneering.
But as Mr. Trump casts doubt on the integrity of the presidential election, there are no signs of a wave of Trump poll watchers building. Like much else about his campaign, his call to “get everybody to go out and watch” the polls seems to be a Potemkin effort, with little or no organization behind it.
Still, his pronouncements about a “stolen” election were enough to draw a mocking rebuke Tuesday from President Obama, who suggested that Mr. Trump’s effort to delegitimize the election results even before the vote takes place was unprecedented. He told the Republican nominee to “stop whining and go try to make his case to get votes.”
“I have never seen in my lifetime or in modern political history any presidential candidate trying to discredit the elections and the election process before votes have even taken place,” Mr. Obama said.
Republican and election officials in cities and states that Mr. Trump has singled out for potential widespread voter fraud, including Philadelphia, Pittsburgh and Ohio, said his message to supporters to become poll watchers had generated scant response.
“There’s a real disconnect between the intensity of the buzz at the national level and anything we’ve seen on the ground,” said Al Schmidt, a Republican who is the vice chairman of Philadelphia’s election board. “We haven’t received a single call from somebody outside of Philadelphia looking to be a poll watcher.”
At rallies since the summer in rural Pennsylvania, Mr. Trump has spoken of the potential for “shenanigans” in Philadelphia, urging supporters to “go around and watch other polling places.”
The type of in-person voter fraud Mr. Trump is warning about is extremely rare; one study by a Loyola Law School professor found 31 known cases out of a billion votes cast in United States elections from 2000 to 2014. Moreover, the ability to commit fraud on a scale vast enough to swing a statewide election would require the coordination of scores of people, a possibility widely dismissed by experts.
His call to monitor polling places betrays an ignorance of election laws in most states, which require poll watchers to be registered in the county or precinct where they operate.
Even though Mr. Trump’s website includes a form to sign up as a poll watcher and “help me stop Crooked Hillary from rigging this election,” local officials in battleground states said they had seen no surge by Trump supporters seeking to be certified poll watchers.
“The numbers this year are on par with the numbers we saw in 2012,” said Katie Eagan, the executive director of the Ohio Republican Party, which is handling the appointment of poll watchers for the Trump campaign throughout the state.
True the Vote, a group dedicated to policing voter fraud that is popular on the political right, said sign-ups for an online training course it offers on how to be a poll watcher were about equal to 2012, some 200 people a day.
Last week outside Pittsburgh, speaking to a nearly all-white audience, Mr. Trump told supporters that it was “so important that you watch other communities, because we don’t want this election stolen from us.”
But even if few are heeding Mr. Trump’s call to sign up as poll watchers, a big question is whether Trump supporters will nevertheless flood polling places on Election Day in Democratic strongholds.
Lisa M. Deeley, a Democrat on the Philadelphia voting board, said she feared that Trump supporters would gather at polling sites, where they are allowed to go within 10 feet of the entrances, to jeer voters.
“It’s one thing for any candidate to say, ‘I need volunteers, come out and support my campaign,’” she said. “But when a candidate is saying, ‘I need your help because they’re cheating,’ it changes the game.”
In general, states permit citizen poll watchers in polling locations to check the work of election officials. Qualifications differ by state, but many require monitors to be registered in the county or precinct where they serve. They can be appointed by political parties, and in some cases by the candidates themselves.
In 39 states, credentialed poll watchers can challenge voters’ eligibility, with the rules varying widely, said Wendy R. Weiser, the director of the Democracy Program at the Brennan Center for Justice.
Pennsylvania, which has a permissive statute, allows challenges to a voter’s photo ID and residency, though the state clarified this year that challenges could not be based on ethnicity or race.
“I think there’s a real risk of improper challenges,” Ms. Weiser said.
Philadelphia officials said Mr. Trump’s insinuation that widespread fraud in past elections would merit fears of a stolen election were groundless. The candidate appears to be echoing a charge by conservative commentators and internet rumors that the 2012 Republican nominee, Mitt Romney, did not receive a single vote in dozens of precincts in Philadelphia or in nearly 20 precincts in Cleveland.
Election officials in Philadelphia said many of these precincts were as small as a single apartment building, and they were in heavily African-American parts of the city. Efforts by newspapers in Philadelphia and Cleveland to find “missing” Romney voters who had been erased from the vote count came up empty-handed.
Voter fraud “does occur,” said Mr. Schmidt, the Republican election commissioner in Philadelphia, who issued a report in 2012 that found a handful of irregularities.
“But what Trump’s talking about is widespread, coordinated efforts to alter the outcome of the election, and that I’ve just simply never seen. It would be very easy to find because it would involve a conspiracy of dozens if not hundreds of people.”
On Tuesday, state officials in Indiana said they were investigatingpossible fraud in thousands of voter registrations that had been altered. And Trump supporters in Pennsylvania say they are on guard to prevent fraud.
“In Pennsylvania, voting irregularity isn’t a myth,” said Greg Manz, the communications director for the Trump campaign in the state. “Appropriate steps should be taken to ensure all applicable rules are enforced so that the elections are free from fraud and voter irregularity this November.”
Mark Landler contributed reporting from Washington, and Ashley Parker from Colorado Springs.