As he trails in the polls with just over 20 days before Election Day, Donald Trump has been railing that the balloting is supposedly “rigged.”

“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!” Trump tweeted Monday morning.

He was pushing back against the GOP leaders and election experts who are expressing dismay over the Republican nominee’s attacks on the legitimacy of the U.S. democratic system.

Many critics have suggested that Trump is laying the groundwork to contest the election, but these sorts of claims are neither new nor out of character for Trump. The celebrity businessman, who has dabbled in a wide range of conspiracy theories, has contended for years that some elections in the U.S. have been fraudulent.

Just this election cycle, Trump has made a number of claims quickly rejected by fact-checkers. Among other charges, he has said polling places would be “rigged” this year. He declared that there was “dishonest early voting” in the Florida GOP primary. He called for an election do-over in the Iowa caucuses. And he’s accused the media of being involved in a massive conspiracy against him.

Donald Trump speaks during a campaign rally in Charlotte, N.C. (Photo: Evan Vucci/AP)

Trump’s statements were particularly outlandish after Mitt Romney lost the 2012 election to President Obama. Trump, who incorrectly thought Romney would win the popular vote but lose the Electoral College, called for a “revolution” against the U.S. constitutional system.

“We can’t let this happen. We should march on Washington and stop this travesty. Our nation is totally divided,” Trump wrote in a string of Nov. 6, 2012, tweets, some of which have since been deleted.

“The phoney [sic] electoral college made a laughing stock out of our nation. The loser one! [sic] He lost the popular vote by a lot and won the election. We should have a revolution in this country! Well, back to the drawing board!” he continued.

The electoral college is a disaster for a democracy. — Donald J. Trump (@realDonaldTrump) November 7, 2012





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In the months after that election, Trump accused the Obama administration of having covered up various “scandals” in order to avoid public backlash before Election Day.

Does anyone really believe that President Obama found out about Petraeus immediately after the election? — Donald J. Trump (@realDonaldTrump) November 19, 2012





I said gas prices would sky rocket after election – Opec payback! — Donald J. Trump (@realDonaldTrump) February 18, 2013





Obama & his people did a brilliant job of delaying these scandals until after the election. Mitt must be going wild thinking about it! — Donald J. Trump (@realDonaldTrump) May 16, 2013





Throughout 2013, Trump claimed that dead voters helped elect Obama.

The polls have shown that DEAD PEOPLE voted for President Obama overwhelmingly and without hesitation – he must be doing something right! — Donald J. Trump (@realDonaldTrump) November 18, 2013





Maybe some of the dead voters who helped get President Obama elected can be brought back to life after signing up for ObamaCare. — Donald J. Trump (@realDonaldTrump) November 18, 2013





More dead people voted in the last election than enrolled in ObamaCare. Congratulations America! — Donald J. Trump (@realDonaldTrump) November 14, 2013





After he lost the Iowa caucuses to Sen. Ted Cruz, R-Texas, Trump called for a do-over.

Trump was upset that Cruz’s campaign had sent official-looking mailers to voters warning them against sitting out the caucuses. Trump also took issue with Cruz’s campaign incorrectly suggesting that another candidate, Ben Carson, had dropped out of the race.

Based on the fraud committed by Senator Ted Cruz during the Iowa Caucus, either a new election should take place or Cruz results nullified. — Donald J. Trump (@realDonaldTrump) February 3, 2016





The State of Iowa should disqualify Ted Cruz from the most recent election on the basis that he cheated- a total fraud! — Donald J. Trump (@realDonaldTrump) February 3, 2016





Trump also suggested that there was “dishonest early voting” in Florida’s GOP primary, where the property magnate was facing off against Sen. Marco Rubio, R-Fla. At the time, local officials said they found no evidence for such a claim.

We are asking law enforcement to check for dishonest early voting in Florida- on behalf of little Marco Rubio.

No way to run a country! — Donald J. Trump (@realDonaldTrump) March 12, 2016





In early August, Trump began suggesting that the November 2016 election would be “rigged” against him. He claimed later that month that the only way he would lose Pennsylvania, which has reliably backed Democratic presidential candidates, would be “if cheating goes on.”

“That’s the way we can lose the state, and we have to call up law enforcement, and we have to have the sheriffs and the police chiefs and everybody watching,” he said then. “The only way they can beat [our movement], in my opinion, and I mean this 100 percent, is if in certain sections of the state, they cheat. OK?”

And Trump has been escalating his conspiratorial claims about the election as he fights back against a wave of scandals engulfing his campaign. An increasing number of women have recently accused Trump of forcibly kissing or groping them years ago.

Trump denied the allegations while asserting that the media outlets reporting on them were doing so in order to sabotage his campaign and elect Hillary Clinton president.

“The election is absolutely being rigged by the dishonest and distorted media pushing Crooked Hillary,” Trump tweeted Sunday, adding, “but also at many polling places – SAD.”