(WASHINGTON) -- In September 2020, as Joe Biden and Donald Trump debated for the first time, moderator Chris Wallace asked how they would reassure Americans the next president would be the legitimate winner that November.
Biden encouraged viewers to vote and said the results would be accepted.
Trump's final words in response: "It's a rigged election."
Four years later, whether American democracy is at stake is all but certain to be a key question at Thursday's debate.
An ABC News/Ipsos poll in May showed "protecting democracy" was among the top four issues for voters but that they were evenly split on which candidate they trusted to do that.
Issue central to both campaigns
Both candidates are making what happened in November 2020 and then a few weeks later on Jan. 6, 2021, central to their 2024 campaigns, albeit in very different ways.
Protecting democracy is an animating theme of Biden's reelection bid, as his team paints Trump as an existential threat to the country's founding principles and the upcoming election as a battle for the nation's "soul."
That was a focus of Biden's speech earlier this month marking the 80th anniversary of D-Day, which, despite being delivered at Pointe du Hoc in Normandy, had a clear message for American viewers tuning in back home.
"American democracy asks the hardest things: to believe that we're part of something bigger than ourselves," Biden said. "So, democracy begins with each of us."
More recently, as Trump huddled with Republicans just steps away from the U.S. Capitol to plot his second-term agenda, the Biden-Harris campaign released a 30-second ad filled with imagery from the Jan. 6 attack by a pro-Trump mob.
"There is nothing more sacred than our democracy," the narrator said. "But Donald Trump's ready to burn it all down."
The campaign told ABC News Senior White House Correspondent Selina Wang that Biden is preparing ways to hold Trump accountable for his track record and remarks he's made on various topics, including his comment that he'd be a dictator on "Day 1."
Trump tries to flip 'threat' on Biden
Trump, meanwhile, is trying to counter that Biden is the "threat to democracy," accusing Biden of weaponizing government and the legal system to prosecute a political opponent.
At the same time, he continues to make his relentless, false claims of fraud in the 2020 election. His assertions have been debunked by his own administration officials, including former Attorney General Bill Barr.
"I think the big thing we have to do is stop the cheating," Trump said just last week in an interview with his former press secretary, Sean Spicer. "We have to stop the fraud."
Trump consistently promises retribution against his political foes over his 2020 loss and portrays himself to his supporters as a martyr following four historic indictments, two of which allege illegal efforts to remain in power.
"I'm being indicted for you," he said this past weekend at the Faith and Freedom Coalition's conference in Washington. "Never forget our enemies want to take away my freedom because I will never let them take away your freedom. They want to silence me because I will never let them silence you."
And he's made Jan. 6 a sort of rallying cry in his campaign, firing up supporters by claiming he would pardon some of those charged or convicted and referring to them as "patriots" and "warriors" -- and even "hostages."
When it comes to the upcoming election, Biden and the White House have committed to accepting the outcome.
Trump told Time magazine last month he believed he would win and thus eliminate the potential for political violence.
But what happens if he doesn't win?
"It depends," he said.