Republican presidential nominee Donald Trump said he's "running against a rigged press" during a campaign rally on Aug. 2 in Ashburn, Va. (The Washington Post)

Donald Trump, trailing narrowly in presidential polls, has issued a warning to worried Republican voters: The election will be “rigged” against him — and he could lose as a result.

Trump pointed to several court cases nationwide in which restrictive laws requiring voters to show identification have been thrown out. He said those decisions open the door to fraud in November.

“If the election is rigged, I would not be surprised,” he told The Washington Post in an interview Tuesday afternoon. “The voter ID situation has turned out to be a very unfair development. We may have people vote 10 times.”

Those comments followed a claim Trump made Monday, to an audience in Ohio, that “the election is going to be rigged.” That same day, in an interview with Fox News Channel’s Sean Hannity, he beseeched Republicans to start “watching closely” or the election will be “taken away from us” through fraud.

Like much of what Trump says, the “rigged” riff defies the recent norms of politics. And it taps into fears that long predate his campaign. One is a growing and unsubstantiated worry that elections are being stolen. The other is a broader unease that regular Americans are being cheated by Wall Street, by Washington and by a duplicitous media.

Those worries have found voice in both parties this year, with Trump and Sen. Bernie Sanders (Vt.) both rallying their supporters during the Republican and Democratic primaries with the assessment that the system is rigged. Now, Trump is reviving the theme to highlight the possibility of voter fraud in November.

Since the 2000 election, which ended in a legal battle that stopped recounts of ballots in Florida, paranoia about the nation’s election system has mushroomed. According to a Pew Research Center survey, just 48 percent of Americans were confident that “the votes across the country were accurately counted” in the 2004 election. After 2012, an election with a wider popular vote margin, that percentage fell to 31 percent. Among Republicans, it was 21 percent.

“The idea that the person who won the presidency did so illegitimately is not new,” said Jesse Walker, the author of “The United States of Paranoia,” a history of conspiracy theories. “What’s new is the possibility of a possible loser in the presidential contest making an issue out of it. I can’t think of another example in the last century.”

Jokes about Democrats counting votes from dead people or bused-in fraudsters are part of the Republican lingua franca. During his unsuccessful presidential bid, Sen. Ted Cruz (Tex.) often encouraged his audiences to bring friends and family to the polls with a joke about Democratic election theft.

“I want you to vote 10 times,” he would say. “Don’t worry — we’re not Democrats.”

In his interview with The Post, Trump offered that his chief concern about fraud was that states without strict identification requirements would see rampant repeat voters. “If you don’t have voter ID, you can just keep voting and voting and voting,” he said. On Fox News, Trump’s only evidence for fraud consisted of “precincts where there were practically nobody voting for the Republican” in the 2012 election.

Republican presidential nominee Donald Trump told supporters in Columbus, Ohio, Aug. 1 that he worries the Nov. 8 election "is going to be rigged." (The Washington Post)

In reality, voter fraud is rare. A 2014 study by Justin Levitt, a professor at Loyola Law School, found just 31 possible instances of fraud over 14 years of elections with a total of 1 billion votes cast. The low Republican vote in some urban centers squares with the low support black voters gave GOP nominee Mitt Romney’s campaign in 2012.

Still, the battle against “voter fraud” has made gains with Republican lawmakers and conservative journalists. Since the 2013 decision in Shelby County v. Holder undid some requirements of the Voting Rights Act, restrictive new voter ID and registration laws have passed through Republican-run states.

Those laws have been challenged successfully in court, with North Carolina, North Dakota and Wisconsin losing cases in the days before Trump made his “rigged” comments. North Carolina Gov. Pat McCrory accused judges of “undermining the integrity of our elections.”

In an interview Tuesday with CBS12 in Florida, Trump seemed to condemn the rulings against the states. “Some bad court cases have come down,” he said. Some of his more freewheeling supporters went even further, with the radio host Alex Jones warning listeners that the Obama administration might cancel the election, and off-again, on-again adviser Roger Stone telling Breitbart News that Trump needed to be ready for a violent post-election contest.

“I think he’s gotta put them on notice that their inauguration will be rhetorical,” Stone said. “I mean civil disobedience, not violence, but it will be a bloodbath. The government will be shut down if they attempt to steal this and swear Hillary in.”

To Ari Berman, a reporter for the Nation and the author of the voting rights history “Give Us the Ballot,” Trump’s worry about “rigging” sounded like an adaptation of something already mainstream among Republicans.

“There’s been a two-decade campaign on the right to drum up fears of ‘voter fraud’ stealing elections,” Berman said. “They’re trying to say that these voting rights victories will lead to more fraud. They want to spin these court victories not as something that’s good for democracy, but something that will hurt democracy. That’s what Trump is buying into.”

At the same time, many supporters of Sanders’s presidential run have argued that the Democratic nomination was effectively stolen from him — another sentiment Trump has tried to exploit. Long before the Democratic National Convention in Philadelphia, Sanders supporters asked whether a purge of New York voters, California’s slow ballot count or the closure of polling places in Arizona’s largest county had suppressed their votes.

“The Bernie Sanders folks don’t believe all the ballots were counted,” Chuck Pennachio, an academic and a Sanders delegate from Pennsylvania, said at a news conference last week. “They don’t believe that the process was clean. If you look at the exit polls, they don’t match up with the results in 11 of the 12 closest states.”

Every theory about how the primaries were stolen has been debunked. The famous New York purge, for example, disproportionately affected nonwhite voters, who had been breaking for Clinton. The same was true of the long lines in Arizona’s Maricopa County, which resulted from a decision by the county’s Republican-run elections team.

But in trying to explain how some early exit poll results diverged from vote totals, debunkers found themselves struggling to convince their listeners. Joe Lenski, the lead pollster for exit poll provider Edison Research, explained to the skeptical left-wing site Counterpunch that Sanders voters and young voters had been more likely to fill out the surveys. That did not stop the spread of theories that millions of Sanders votes might have been switched or suppressed. Last week, when more than 200 Sanders supporters invaded a media tent at the DNC, some left behind charts attempting to prove that vote-counters skewed the election.

Clinton’s 2.9 million-vote margin in the primaries may have set the upper bounds for speculation that an American election had been stolen. Sanders supporters also latched onto internal emails between staff members at the Democratic National Committee, in which they speculated about a Clinton nomination even before the primaries were over.

Trump, who previously accused Republicans of rigging primaries through the delegate selection process, found solace in the email scandal. Like Sanders, whose voters he wants to convert, he had found the idea of a rigged process syncing perfectly with his outsider brand. On Fox News, Trump tried to tell Sanders’s supporters that they already had seen an election wrested away by the political elite.

“It was rigged a little bit [against] me, and we won,” he said. “It was rigged a little bit against Bernie Sanders.”

“We know it was rigged,” Hannity said. “We’ve seen the emails.”

Philip Rucker contributed to this report.