Washington (AFP) - The US presidential election of 2000 hinged on a few votes in Florida and was ultimately decided in the Supreme Court.

The 2020 White House contest gave birth to the "Big Lie" and saw supporters of the losing candidate storm the US Capitol.

Just wait and see what 2024 has in store.

Donald Trump, the first president in US history to refuse to accept the outcome of an election, is flirting with another White House run in what could be a make-or-break moment for American democracy.

Robert Kagan, a senior fellow at the Brookings Institution, set alarm bells ringing in political circles last week with a chilling doomsday scenario opinion piece in The Washington Post.

"The United States is heading into its greatest political and constitutional crisis since the Civil War," Kagan wrote.

The neoconservative scholar warned of a "reasonable chance over the next three to four years of incidents of mass violence, a breakdown of federal authority, and the division of the country into warring red and blue enclaves."

Polls suggest a majority of Americans share at least some of Kagan's concerns: 56 percent of the respondents in a recent CNN-SSRS survey said US democracy is under attack.

Thirty-seven percent said it is being "tested." Only six percent said it is in no danger.

Trump's unceasing and unfounded claims that the November 2020 presidential vote was "stolen" by Democrat Joe Biden have seeped into the political bloodstream.

Seventy-eight percent of the Republicans surveyed by CNN-SSRS said they do not believe Biden legitimately won the presidency, a figure in line with the findings of other opinion polls.

"It's a new phenomenon in American elections," said Edward Foley, a constitutional law professor at The Ohio State University.

"There have been fights over hanging chads -- like Bush vs Gore in 2000 -- and there have been recounts for as long as there have been elections in America," Foley said.

"But the 'Big Lie' is a new thing. It's disconnected from reality and it's kind of a social pathology."

'By whatever means necessary'

Richard Hasen, a law and political science professor at the University of California, Irvine, said in a recent research paper that the United States finds itself in a moment of "democratic peril," facing an unprecedented danger of "election subversion."

"The United States faces a serious risk that the 2024 presidential election, and other future US elections, will not be conducted fairly, and that the candidates taking office will not reflect the free choices made by eligible voters under previously announced election rules," Hasen wrote.

In his opinion piece, Kagan said the 75-year-old Trump and his Republican allies are laying the groundwork to ensure a 2024 victory "by whatever means necessary."

Trump, who retains an iron grip on the Republican faithful and is all but certain to be the party's presidential nominee if he does decide to run, appears to be setting the stage for the "Big Lie 2.0," said Foley.

The strategy involves restrictions such as voter identification laws passed by the legislatures of some Republican-led states which Democrats claim are intended to suppress the minority vote and Republicans say are designed to protect the integrity of the ballot.

It also includes replacing Republican state election officials such as Brad Raffensperger, the Georgia secretary of state who refused to do Trump's bidding in 2020 and "find" 11,780 votes, with candidates who are diehard supporters.

"Once you have that person in charge you have somebody who has great influence on how the election is conducted, how the votes are counted, who's declared the winner, how the Electoral College votes align," said Larry Sabato, director of the Center for Politics at the University of Virginia.

'Ultimate perversion of democracy'

While it would spark Democratic outrage, Republican-controlled state legislatures could potentially ignore the popular vote in their states if it goes against Trump and appoint their own electors to the Electoral College, the final arbiter of who wins the presidential race, Sabato said.

Republicans are also well-positioned to win a majority in 2022 in the currently Democratic-controlled House of Representatives, giving them another potential lever of power in 2024.

"As ugly as last January 6 was with bloodshed and insurrection the outcome was never in doubt," Foley said, as then vice president Mike Pence ultimately refused to go along with Trump's demands that he reject the Electoral College slates from several states they lost to Biden.

"But if members of Congress on January 6, 2025 are predisposed to the 'Big Lie' approach, and are willing to repudiate election results just for the sake of pure political power, that would be the ultimate perversion of democracy," Foley said.