Joe Biden and Donald Trump will be desperate to avoid any slip-ups as they prepare to face off for the first time in the 2024 election campaign.
US President Mr Biden will get the chance to reassure voters at a CNN TV debate on Thursday night that he is still capable of leading the US on the world stage amid the wars in Ukraine and Gaza, despite growing questions about whether he remains mentally sharp enough at the age of 81.
It follows a number of embarrassing incidents for the President, who recently appeared to freeze during a concert at the White House to celebrate the Juneteenth holiday earlier this month.
Meanwhile convicted felon Mr Trump will try to convince voters that he is still suited to return to the Oval Office after being found guilty of 34 charges in his porn star hush money trial.
The 78-year-old is the first former US president to be criminally convicted and faces sentencing on July 11.
Both candidates are disliked by majorities of Americans, according to polling, and offer sharply different visions on virtually every core issue.
Audiences will be looking at for missteps by both candidates, with one expert quipping: “People are going to watch this like they watch a NASCAR race, - it is going to be fairly boring unless there's car crashes.”
Mr Trump has promised sweeping plans to remake the US government if he returns to the White House, while Mr 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 on the debate stage on Thursday night have the rare potential to alter the trajectory of the race.
Mr Trump and Mr Biden have not been on the same stage or even spoken since their last debate weeks before the 2020 presidential election.
Mr Trump skipped Mr Biden's inauguration after leading an unprecedented and unsuccessful effort to overturn his loss to Mr Biden that culminated in the January 6 Capitol riots by his supporters.
Thursday's broadcast on CNN will be the earliest general election debate in history. It is 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 match-up since 1988.
Aiming to avoid a repeat of their chaotic 2020 match-ups, Mr Biden insisted - and Mr 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.
The wars in Ukraine and Gaza 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 Mr Trump is legally immune for his alleged role in the January 6 Capitol riots.
That is weeks after Mr 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.
Mr Biden spent the week leading up to the debate with senior White House and campaign aides, advisers and allies.
A mock stage was built to simulate the studio where the debate will be held, and Mr Biden's personal lawyer, Bob Bauer, was reprising his role as Mr Trump in practice sessions.
Aides say the work reflects Mr Biden's understanding that he cannot afford a flat showing. They insist the sometimes stodgy orator would rise to the occasion.
Mr 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.
