WASHINGTON - Roughly three weeks before Americans go to the polls, Republican presidential nominee Donald Trump is telling supporters that the election is “rigged” against him.

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

Should Trump lose to Democrat Hillary Clinton on November 8, it remains to be seen whether he would concede or claim that the election was stolen from him.

If he refuses to deliver a concession speech, Trump would break with a time-honored tradition in American politics.

“I have just called President Obama to congratulate him on his victory,” said 2012 Republican nominee Mitt Romney on election night four years ago.

Even in 2000, after the most hotly-contested election result in modern U.S. history, Democrat Al Gore conceded to Republican George W. Bush once the Supreme Court halted vote recounts in Florida, handing Bush a miniscule margin of victory.

“I spoke with George W. Bush and congratulated him on becoming the 43rd president of the United States,” Gore said in nationally-televised remarks. “I accept it.”

As is also customary, Gore called for national unity after a hard-fought and bruising campaign.

“I also accept my responsibility,” Gore said, “to honor the new president-elect and do everything possible to help him bring Americans together in fulfillment of the great vision that our Declaration of Independence defines and that our Constitution affirms and defends.”

Supporters of Republican presidential candidate Do
Supporters of Republican presidential candidate Donald Trump yell at reporters as they arrive for a campaign rally, in Cincinnati, Ohio, Oct. 13, 2016.

Hardening position

Would Donald Trump be gracious in defeat?  Last month, in the first presidential debate, he said he would accept the outcome of the election.

"The answer is, if she wins, I will absolutely support her," Trump said.

His message of recent days has sounded markedly different.

“It is a rigged system, folks,” Trump said Saturday at a rally in Maine.

Stung by a media firestorm over allegations of sexual misconduct, fueled by his own words as well as those of multiple accusers, Trump cast himself as the victim of a smear campaign to deny him the presidency.

“The election is being rigged by corrupt media pushing false allegations and outright lies in an effort to elect Hillary Clinton president,” he said.

In recent weeks, Trump has also issued veiled warnings about fraud at polling places.

“Go and vote and then check out areas,” he told supporters in Pennsylvania.  “Because a lot of bad things happen.  And we do not want to lose for that reason.”

Democrats see a candidate willing to tear at the threads of democracy rather than accept responsibility for his own shortcomings.

“He is blaming the media, he is blaming the GOP (Republicans),” said Democratic vice presidential nominee and Virginia Senator Tim Kaine on ABC’s This Week program. “He is saying that America cannot run a fair election.  He is swinging at every phantom of his own imagination because he knows he is losing.”

Republican presidential candidate Donald Trump sta
Republican presidential candidate Donald Trump stands on stage with female supporters during a campaign rally in Charlotte, North Carolina, Oct. 14, 2016.

Some backers say ‘ready for a revolution’

But Trump’s backers say he has a point – that the news media have been more focused on controversies surrounding Trump than on wave after wave of revelations from WikiLeaks about Clinton’s paid speeches to Wall Street and what are believed to be email communications within her campaign.

“This election is being rigged by the national media, who are doing everything they can to suppress bad news about Hillary, and everything to maximize bad news about Trump,” said former House speaker Newt Gingrich, also on ABC.

Agitation runs high among some of Trump’s most ardent supporters, as his running mate, Indiana Governor Mike Pence, discovered at a recent campaign stop.

“If Hillary Clinton gets in, I myself am ready for a revolution,” one rally attendee said in a question-and-answer session with Pence.

“No, do not say that,” the Republican vice presidential nominee replied.

Some Republican leaders are uncomfortable with Trump’s latest line of attack.  A spokeswoman for House Speaker Paul Ryan issued a statement saying, “Our democracy relies on confidence in election results, and the speaker is fully confident the states will carry out this election with integrity.”