CHICAGO (AP) — Monday night could not have gone better for online troublemakers who have spent years propagating false or misleading conspiracy theories on the internet that the U.S. election is rigged or vulnerable to tampering.

The delayed election results from the Iowa caucuses revealed some Democratic candidates’ supporters are so distrustful of the outcome that they peppered the internet with unproven claims that accused the Democratic Party of corruption by attempting to tilt the election in favor of a single candidate.

President Donald Trump and his supporters seized on that distrust by sending tweets Monday night with #RiggedElection. Trump’s own sons shouted “Rigged!” at an Iowa campaign event. And Republican Sen. Lindsey Graham suggested in a tweet that the caucus issues were the result of a “Bernie blowout.”

It’s the type of conspiracy theory that experts fear will dog this year’s presidential race until Election Day.

“Democracy depends on the losers accepting election results,” said University of California, Irvine, professor Richard Hasen, whose book “Election Meltdown” was published Tuesday in what he said was an ominous coincidence. “Now we’re starting off the election season with seeds of doubt, which is terrible.”

In recent months, social media users have promoted conspiracy theories around the legitimacy of election results around the country, from a gubernatorial race in Kentucky to statehouse races in Virginia.

The tweets Monday began spreading minutes after the Iowa Democratic Party announced it was reviewing results for “quality control.” The app used by the Iowa Democratic Party to collect results Monday experienced technical glitches that left the caucus results in limbo through Tuesday.

“Quality control = rigged?” Trump campaign manager Brad Parscale said in a tweet that has since been shared and liked more than 20,000 times.

As the delay of final results continued into Tuesday, social media users spread theories of complex schemes that were deployed to keep the results hidden in order undermine certain Democratic candidates such as Sen. Bernie Sanders. Many of the tweets suggested the Democratic Party or the Democratic National Convention intentionally bungled the caucus results, even though the Iowa Democratic Party administered Monday’s caucus.

“Iowa is just the start guys,” wrote one Twitter user, who has a profile picture of himself in a Sanders T-shirt. “The Democratic Party will not allow Bernie to win.”

The online conspiracy theories, in some cases, were based on easily debunked or misleading claims.

For example, Facebook and Twitter posts falsely suggested that former Democratic presidential candidate Hillary Clinton, Sanders’ opponent in the 2016 primary, had a hand in developing the ill-fated app used to collect the Iowa results. Further fueling that distrust was that three of the senior executives at Shadow Inc., which created the app, previously worked for Clinton’s failed campaign.

Some posts, which were shared thousands of times, accused former Clinton campaign manager Robby Mook of creating the app.

In a tweet, Mook said he “did not have” anything to do with building the caucus app. Mook did not immediately return a request from The Associated Press for comment.

Other online posts placed blamed the problem on a new culprit: Democratic presidential candidate Pete Buttigieg, the former South Bend, Indiana, mayor who unsuccessfully ran to be the Democratic Party’s chairman three years ago.

Some social media users insisted he had pulled off a scam to delay the results with the help of party insiders. Others wrongly asserted that Buttigieg’s campaign had developed the app used for the Iowa caucuses. Other social media posts pointed out that the founder of a nonprofit organization that launched Shadow Inc. last year is married to a senior adviser for Buttigieg’s 2020 campaign.

By Tuesday morning, #MayorCheat was trending on Twitter, where it was mentioned more than 120,000 times by the afternoon.

The hashtag was first sent by verified Twitter accounts, according to an analysis by Ben Nimmo, a disinformation and security expert for social media analysis firm Graphika. As of Tuesday, there were no signs that foreign accounts were promoting the hashtag, he added.

“This is Americans trolling Americans,” Nimmo said. “That’s the really worrying thing in 2020.”

That misinformation is partly rooted in the fact that Buttigieg’s campaign has paid Shadow Inc., the company behind the Iowa caucus app, for software.

Buttigieg’s campaign paid $42,500 to Shadow Inc. for text messaging software in July. Other Democrats, including former Vice President Joe Biden, Sen. Kirsten Gillibrand and the Texas Democratic Party, have contracted with Shadow for similar services, federal campaign finance data show.

The Buttigieg campaign did not help develop the app used in Iowa, a campaign spokesman confirmed Tuesday to the AP.

In a statement on Twitter, Shadow Inc. apologized for the delays and confirmed it had “contracted with the Iowa Democratic Party to build a caucus reporting mobile app for local officials to use” Monday.

State fundraising reports from Iowa’s Democratic Party show party officials paid more than $63,000 to the same firm in November and December for “professional fees.”

The Iowa results were backed up by paper ballots, which is what the Iowa Democratic Party is using to verify the results. Figures reflecting 71% of precincts in the state were released by Tuesday night.

Virginia Sen. Mark Warner, a Democrat who is vice chairman of the Senate Select Committee on Intelligence, warned that foreign groups looking to destabilize the U.S. could try to exploit the doubts and fears spread online over the Iowa results. He said the Iowa episode should serve as an “early warning sign” that Congress, local election officials and social media platforms must do more to protect election integrity.

“It does … reinforce the fact, as we have started to see over the internet, conspiracy theories pop up, that whether domestic or foreign efforts to undermine confidence in our elections, that those threats are out there,” Warner said to reporters Tuesday.

In November, for example, social media posters exaggerated small-scale voting problems in Kentucky to suggest the results of the governor’s race were spoiled by dead people voting or misprinted ballots. The now-former Republican Gov. Matt Bevin requested a recanvass of the results because of what he said were “irregularities” after the initial vote tally put his reelection bid behind by 5,000 votes — but he refused to provide evidence of those problems. Bevin, a Republican, later conceded to now-Gov. Andy Beshear, a Democrat.

These type of cases show it’s important for the presidential candidates to foster trust in the system among their supporters, said Charles Stewart III, a political science professor at the Massachusetts Institute of Technology.

“I really wish and hope that the candidates will recognize that if they don’t defend the system when it can be defended that they are doing harm to democracy and doing harm to devalue the nomination they’re seeking,” Stewart said.