“If I lose - I’ll tell you what, it’s possible. Because they cheat. That’s the only way we’re gonna lose, because they cheat," Trump said at a Michigan rally in September.
A refusal by Trump, 78, to accept victory by current vice president and Democratic rival Kamala Harris, 59, could throw the United States into political instability at a time when the country is already deeply divided.
After Trump lost the 2020 election, he and his allies attempted to overturn the result through dozens of lawsuits that ultimately failed to alter or delay the vote count.
He also pressured officials in Georgia to find more votes for him; and his supporters stormed the US Capitol on January 6, 2021 in a failed effort to stop his vice president, Mike Pence, from certifying Biden's victory.
One key difference this time is that Trump does not have the presidential levers of power that he did in 2020. And new state and federal laws have been put in place to make it more difficult to influence election results.
Still, Trump and his allies have been laying the groundwork for months to cry foul if he loses on November 5. He could contest a win by Harris in the courts or raise doubts about the validity of her victory among supporters that could have unforeseen consequences.
SMOKE AND MIRRORS
Republicans and Democrats expect that vote counting could drag on for several days after November 5 as mail-in ballots are tabulated and other votes are tallied and verified.
If it appears Trump, 78, is losing, the delay will give him an opportunity to claim fraud and attempt to undermine confidence in election officials, while also possibly encouraging his supporters to protest.
He has already threatened to jail election workers and other public officials for “unscrupulous behaviour,” although he would need to win the election first.
Trump can take his case directly to the American public without waiting for proof, using social media, news conferences and interviews.
"President Trump has been very clear that we must have a free and fair election," said Karoline Leavitt, a spokesperson for the Trump campaign.
The Harris campaign did not immediately respond to a request for comment.
IN THE BATTLEGROUNDS
Republicans have already pre-emptively filed more than 100 lawsuits in the battleground states that will decide the election to seed the ground for post-election challenges, including claiming, without evidence, that non-citizens will be voting in large numbers.
Both parties plan to dispatch thousands of trained volunteers called poll watchers to monitor voting and vote counting with a mandate to report any irregularities.
Some voting rights activists are concerned that Republican poll watchers could be disruptive, but the Republican Party says the volunteers have been trained to stay within the law.
As they did in 2020, Trump's allies in key states - local election officials, state lawmakers and perhaps judges - could seek to delay certification, the confirmation of a state's official tally, through claims of fraud.
Those efforts did not succeed last time, and election law experts say the laws in those states are clear that local officials lack the power to throw out ballots or derail the process.
Five of the seven battleground states have Democratic governors but Democratic activists worry about Georgia, whose state election board recently gave unprecedented authority to local officials to conduct inquiries, a move they say could give an opening to bad-faith actors who attempt to contest or delay the vote count.
A Georgia judge, however, ruled this week that local officials must certify the results and do not have the discretion to do otherwise.
All states must submit their certified totals before the Electoral College meets in December and electors cast their votes. That vote is then delivered to Congress for final certification in January.
Trump-inspired court challenges and certification delays could cause a state to miss the filing deadline. That could provide grist for Republican objections in Congress.
Some election law experts caution that it is difficult to predict how novel legal disputes over certification might be resolved, especially if they are handled by judges sympathetic to Trump's claims.
CONGRESS HAS FINAL SAY
After the 2020 election, Congress passed a reform law that makes it more difficult for candidate to mount the kind of challenge Trump attempted.
It makes clear that the vice president, who in this case would be Harris, has no authority to delay national certification or throw out a state's results, as Trump urged Pence to do in 2020.
The measure also requires that an objection to a state's electoral count cannot be brought unless one-fifth of the members of each house of Congress agrees. After that, it takes a majority vote in each house for an objection to be found valid.
In the unlikely result that enough electoral votes are tossed so that neither candidate reaches the necessary majority, the newly elected U.S. House of Representatives would choose the next president.
CIVIL UNREST
Any effort by Trump to suggest the election was rigged could potentially lead to civil unrest, as it did on January 6, 2021.
Experts who monitor militant right-wing groups, such as Peter Montgomery of the People For the American Way, a liberal think tank, say they are less concerned about a violent response from these groups than they are about threats against election workers counting votes.
There also could be violent demonstrations in the capitals of battleground states, Montgomery said.
Hundreds of people who were involved in the Jan. 6 attack on the Capitol have been convicted and jailed for their actions, a powerful deterrent to others who may be considering taking similar actions.
