How Biden-Trump debate could change trajectory of 2024 campaign

US President Joe Biden and his Republican rival, Donald Trump, will meet for a debate on Thursday that offers an unparalleled opportunity for both candidates to try to reshape the political narrative.

Biden, the Democratic incumbent, gets the chance to reassure voters that, at 81, he's capable of guiding the US through a range of challenges.

The 78-year-old Trump, meanwhile, could use the moment to try to move past his felony conviction in New York and convince an audience of tens of millions that he's temperamentally suited to return to the Oval Office.

Biden and Trump enter the night facing fierce headwinds, including a public weary of the tumult of partisan politics.

Both candidates are disliked by majorities of Americans, according to polling, and offer sharply different visions on virtually every core issue.

Trump has promised sweeping plans to remake the US government if he returns to the White House and Biden argues that his opponent would pose an existential threat to the nation's democracy.

With just over four months until Election Day, their performances have the rare potential to alter the trajectory of the race.

Every word and gesture will be parsed not just for what both men say but how they interact with each other and how they hold up under pressure.

"Debates tend not to change voters' perception in ways that change their vote: They ordinarily reinforce, not persuade," said Kathleen Hall Jamieson, the director of the Annenberg Public Policy Center at the University of Pennsylvania and an expert on presidential communications.

"What makes this debate different is that you have in essence two incumbents about whom voters have very well-formed views. But that doesn’t mean that those perceptions are right or match what voters will see on stage."

The debate marks a series of firsts

Trump and Biden haven't been on the same stage or even spoken since their last debate weeks before the 2020 presidential election.

Trump skipped Biden's inauguration after leading an unprecedented and unsuccessful effort to overturn his loss to Biden that culminated in the 6 January 2021 Capitol insurrection by his supporters.

Thursday's broadcast on CNN will be the earliest general election debate in history.

It's the first-ever televised general election presidential debate hosted by a single news outlet after both campaigns ditched the bipartisan Commission on Presidential Debates, which had organised every matchup since 1988.

Under the network's rules, independent candidate Robert F. Kennedy Jr did not qualify.

Aiming to avoid a repeat of their chaotic 2020 matchups, Biden insisted – and Trump agreed – to hold the debate without an audience and to allow the network to mute the candidates' microphones when it is not their turn to speak.

There will be two commercial breaks, another departure from modern practice. The candidates have agreed not to consult staff or others while the cameras are off.

The timing follows moves by both candidates to respond to nationwide trends toward early voting by shifting forward the political calendar.

It remains to be seen whether the advanced schedule will dampen the effects of any missteps or crystallise them in the public's mind.

"You have two men that have not debated in four years," said Phillippe Reines, a Democratic political consultant who helped former Secretary of State Hillary Clinton prepare for debates with Trump in 2016.

Biden and Trump, he said, "don't like each other, haven't seen each other, [are] pretty rusty heading into the biggest night of their lives. That about sums up what's at stake on Thursday."

Both sides recognize the stakes

The debate falls days after the second anniversary of the Supreme Court's overturning of Roe vs Wade, ending a federally guaranteed right to abortion and pushing reproductive rights into the centre of politics ever since.

The face-off also occurs just after the Biden White House took executive action to restrict asylum claims at the US-Mexico border in an effort to lower the number of migrants entering the country.

Trump has made irregular immigration a centrepiece of his campaign.

The Ukraine and Gaza wars loom over the race, as do the candidates' sharply differing views about America's role in the world and its alliances.

Differences on inflation, tax policy, and government investment to build infrastructure and fight climate change will provide further contrasts.

Also in the political background: The Supreme Court is on the brink of announcing its decision on whether Trump is legally immune for his alleged role in the 6 January 2021 insurrection.

That's weeks after Trump was convicted in New York of taking part in a hush money scheme that prosecutors alleged was intended to unlawfully influence the 2016 election.

Biden spent the week leading up to the debate secluded at Camp David with senior White House and campaign aides as well as a coterie of longtime advisers and allies.

A mock stage was built at the compound to simulate the studio where the debate will be held, and Biden's personal attorney, Bob Bauer, was reprising his role as Trump in practice sessions.

Aides say the work reflects Biden's understanding that he can't afford a flat showing. They insist the sometimes stodgy orator would rise to the occasion.

Trump, meanwhile, has continued his more unstructured debate prep with two days of meetings at his Florida estate, phoning allies and supporters, and road-testing attacks in social media postings and in interviews with conservative-leaning outlets.

Trump and his aides have spent months chronicling what they argue are signs of Biden's diminished stamina. In recent days, they've started to predict Biden will be stronger on Thursday, aiming to raise expectations for the incumbent.

The candidates have Georgia on their mind

Atlanta, the debate's host city, offers symbolic and practical meaning for the campaign, but each side believes that what happens there will resonate far and wide.

In 2020, Biden secured Georgia's 16 electoral votes with a margin of less than 12,000 votes out of five million cast.

Trump pushed the state's Republican leadership to overturn his victory based on false theories of voter fraud, memorably being caught on tape saying he wanted to "find 11,780 votes".

He now faces state racketeering charges.

Both campaigns held a flurry of events in Atlanta leading into the debate, including competing events at Black-owned local businesses.

Trump called in Friday to a gathering at Rocky's Barbershop in the Buckhead community to talk about his matchup with Biden and question whether CNN moderators Jake Tapper and Dana Bash would treat him fairly.

Heading out of the debate, both Biden and Trump will travel to states they hope to swing their way this fall.

Trump is heading to Virginia, a onetime battleground that has shifted toward Democrats in recent years.

Biden is set to jet off to North Carolina, where he is expected to hold the largest-yet rally of his campaign in a state Trump narrowly carried in 2020.