The United States is preparing for another toss-up presidential election in which one candidate may not accept the results and could instead declare a preemptive victory.

Though Kamala Harris has led the popular vote polling average by a percentage point or two, the Electoral College system used in the United States currently favors Republicans and their candidate, Donald Trump. Seven swing states are projected to decide the presidency.

With a combination of tight polling, a patchwork of rules across 10,000 voting jurisdictions, and the likelihood that a true winner may not become clear for days, some observers are concerned that Trump might once again call an early victory.

Trump has been preparing the groundwork to dispute the result since the last election. He's repeatedly accused electoral authorities of allowing fraudulent votes, and his opponents of cheating. He's sought to undermine perceptions of American elections being "free and fair."

So what are the risks and which safeguards are in place to preserve the electoral process?

What happened in 2020?

In the first sign Trump had lost the 2020 election, Fox News, which typically supports Republican candidates, declared Joe Biden had won Arizona.

Trump decried the media's role in calling the results, despite the press having a near-200-year tradition of projecting results in American elections. He claimed that the election was "rigged" and stolen from him, despite no proof of electoral misdemeanors.

It led to the Capitol Hill riots on January 6, 2021 when some of his supporters stormed the Capitol building to try and prevent the certification of Biden's victory.

Trump and his supporters eventually filed more than 60 lawsuits in various courts challenging the results. Only one of those ruled in his favor which did not materially affect either local or state results in favor of Biden.

Observers widely accepted the 2020 election as free and fair. This year, electoral authorities have said voter fraud is a rare occurrence.

"The system itself, overall, held up actually surprisingly well," Robert Tsai, a professor of law at Boston University, says of the 2020 result.

"There are still structural things in place where, if Donald Trump tries to declare [early] victory again, it'll still be hard to pull it off."

What happens if Trump declares an early victory?

While polls predict a down-to-the-wire election, a normal polling error (all polls have a margin of error in their calculations) means either candidate could also win in a landslide.

Assuming polls are right and Trump claims an early victory with key states undecided, a few things are likely to happen.

First, most people are still informed by media outlets calling the race. These outlets use a combination of data provided by polling agencies and in-house analysis to project results.

That the Republican-leaning Fox News was the first to declare Biden had won Arizona in 2020 is an indication that traditional biases are cast aside during elections in favor of accurate calling.

The Democrats have already said they're on standby with a social media campaign to counter a premature victory declaration. Vice President Kamala Harris told ABC News last Wednesday "if he [Trump] does and, if we know that he is actually manipulating the press and attempting to manipulate the consensus of the American people ... we are prepared to respond."

Even voters expect Trump to reject results that aren't in his favor. A CNN poll found just 30% of registered voters think Trump would accept the results if he lost, in contrast to 73% that felt Harris would accept a defeat.

Ultimately, each state has rules on how votes are counted and winners confirmed. This process will continue until all states and Washington D.C. have declared their results.

"A candidate can proclaim victory as much as they want, but if the vote totals are not there for that candidate, that candidate is going to lose," says Richard Pildes, a constitutional law specialist at NYU.

"There are no legal consequences from candidates doing any of this [declaring early victory], there are cultural consequences, if you will, or maybe political consequences," he said.

Can a candidate contest the election? 

There's nothing to stop any candidate from contesting the election.

Just as in 2020, when Trump and his supporters lodged multiple legal challenges to the election proceedings, a candidate has to submit their protest in the courts.

The Republican National Committee has reportedly mounted 130 legal challenges already, mostly in swing states. The Democrats have also appointed legal teams across the country to counter Republican claims of voter fraud.

"Those challenges would be brought in the courts and I certainly expect to see some of them depending on how close the election is," Pildes said.

"There's nothing wrong with that, we want disputes to be settled by law, we want them to be settled in the court, not in other venues, so as long as there's the appropriate factual and legal foundation for raising certain issues after the election in the courts, that's fine. That's a right candidates have," he added.

Staging attacks would be much harder in 2024

Are scenes reminiscent of those seen in 2021 when rioters rushed the Capitol Building likely again?

Tsai doesn't think so. For one thing, Biden will remain president until his successor is inaugurated. Trump, Tsai says, isn't in the White House "so he can't just refuse to vacate."

"It's much harder to raise a ruckus when you can't lean on people from the Oval Office."

But it doesn't mean that preexisting perceptions of an unfair vote couldn't fuel unrest, Tsai explained, adding that "it's hard to imagine that the Biden [administration] Department of Justice isn't already on high alert."

Tsai points out that Biden's team has informed certain states "that they want to have a presence in certain jurisdictions within those states because of things that have happened in the past or because of certain things they've detected, largely through the FBI."

"If there was truly any risk of any high-level insurrectionist activity of that sort I think we've already got the resources to be able to step in and intervene," Tsai said.

 Edited by: Andreas Illmer