Much of the outside world's focus during the 2024 US election has been on what victory for former United States president Donald Trump might look like, but many Americans, including some of his most vocal opponents, are fretting about the opposite outcome.

The 78-year-old Republican, who is in a dead heat with Democrat Kamala Harris in the race for the White House, has never acknowledged the legitimacy of his election defeats from the 2016 Iowa primary to his presidential contest in 2020.

His denialism deeply polarised the country last time around, and his continued attempts to sow distrust in US democracy have sparked fears of a repeat of the violence seen during the 2021 storming of the US Capitol.

"Should he lose this year, I have no doubt that he will claim fraud, leave no stone unturned to reverse the results, and refuse to attend Harris's inauguration," said Donald Nieman, a political analyst at Binghamton University in New York state.

"He's not only a sore loser, he's someone who will never admit he lost."

Trump's rap sheet demonstrates that it is not beyond him to try to cheat in elections.

He has 34 felony convictions for a scandal involving covered-up payments to silence an adult film star he feared was about to wreck his 2016 campaign with a salacious story about a one night stand.

And he has been indicted twice and impeached twice over alleged efforts to steal or otherwise cheat in the 2020 election, which he still has not conceded.

Rejected by the American people four years ago, Trump and his allies flooded the zone with bogus claims of irregularities and fraud.

Deadly riot

Trump's critics worry about a repeat of the deadly January 6 riot which was carried out by an angry mob summoned to Washington by Trump, pumped up by his claims of voter fraud and sent marching on the Capitol.

Especially since he's at it again.

"If I lose, I'll tell you what, it's possible because they cheat. That's the only way we're going to lose — because they cheat," Trump told rally-goers in Michigan last month.

Trump has been dusting off the same baseless concerns over the legitimacy of vote counts, foreigners voting, the reliability of mail-in ballots and much else.

The ex-president and his allies set the stage for the 2021 riot through legal means — more than 60 lawsuits largely complaining about the way state and local authorities had changed voting rules to take account of a raging pandemic.

But they lost every substantive case, with judges ruling that objections to election organisation should have been lodged long before the first ballot was cast.

Republicans hit the ground running this time around, filing more than 100 lawsuits before early voting began about every aspect of the election, from how Americans register and cast ballots to who can vote.

Many of the suits seek to limit access to the polls and most will be unresolved by Election Day, but experts say this plays into distrust over vote-counting that Trump and other conspiracy theorists have spent years exacerbating.

Almost two-thirds of Americans are anticipating post-election violence, a Scripps News/Ipsos poll out Thursday found, and most support using the military to quell unrest after polls open on November 5.

More than a quarter believe that civil war could break out, according to a new YouGov poll, with 12% saying they know someone who might take up arms if they thought Trump had been cheated.

The intelligence community raised concerns about the potential for bloodshed in a report on election threats from foreign actors that was declassified, redacted and released last week by the Office of the Director of National Intelligence.

"Foreign-driven or -amplified violent protests, violence, or physical threats... could challenge state and local officials´ ability to conduct elements of the certification and Electoral College process," it said.

Security measures have been beefed up in Washington in anticipation of potential unrest, although analysts contacted by AFP saw a repeat of the 2021 insurrection in the capital as unlikely, with hundreds of subsequent prosecutions acting as a potent deterrent.