The two oldest candidates ever to run for US president meet on Thursday for a televised debate unlike any other. One accuses his rival of being unhinged and a danger to democracy, while the other accuses his opponent of being senile and corrupt.
US president Joe Biden, 81, and former president Donald Trump, 78, are essentially tied in national opinion polls with fewer than five months until the November 5th election. But many voters remain undecided, raising the stakes of a debate that will be viewed more for possible moments of drama than for policy discussions between the Democratic president and his Republican challenger.
Here is what to watch for in the first 2024 presidential debate broadcast from Atlanta on CNN at 9pm EDT on Thursday (0100 GMT on Friday).
The fitness question
Both candidates may face questions about their fitness to serve in ways previous presidential hopefuls have not. Mr Trump claims Mr Biden is physically and mentally unfit for office, while Mr Biden has called his predecessor "unhinged" and a danger to democratic norms. Democrats point to Mr Trump's role in the January 6th, 2021, attack on the US Capitol by his supporters, his other efforts to overturn the 2020 election and his conviction on May 30th on 34 felony counts for his involvement in a hush money scheme to keep an alleged sexual encounter with a porn star from the public.
Mr Biden’s mental and physical strength has been the subject of scrutiny and speculation as he seeks a second four-year term. Critics say he is slowing down and point to a series of verbal slip-ups.
Allies maintain he is as sharp as ever. Mr Trump has regularly mocked Mr Biden at rallies, suggesting he’s not up to the job. The president’s age is also on most voters' minds, including Democrats, and many viewers will be on alert for any sign that Mr Biden - or Mr Trump - is not up to the task.
Mr Trump has not faced the same questions about his stamina but has raised eyebrows with his tendency to go off on extended tangents and occasionally mixing up names and misidentifying Mr Biden as former president Barack Obama.
The temperament test
Both candidates are known for their tempers and impatience. They are used to commanding the stage and getting their way. Both have been president and likely see little reason to yield to the other.
"There is a lot of bad blood," said Tevi Troy, a former George W Bush official who helped that Republican president prepare for the 2004 debates against Democrat John Kerry.
Mr Biden rattled Mr Trump during their first debate in the 2020 race, leading Mr Trump into what was viewed as a poor performance as the Republican repeatedly interrupted and bickered with the moderator. Mr Biden went on to beat Mr Trump handily.
Mr Trump may try to get under Mr Biden’s skin by mentioning the legal problems of the president's son, Hunter, who was convicted of lying about his drug use to illegally buy a gun.
Mr Trump has to be careful, too, not to turn off moderate voters with a bullying approach.
“You can’t be so aggressive that you are rude, and you seem to be trampling your opponent,” said Brett O’Donnell, a veteran Republican debate consultant.
Both Mr Biden and Mr Trump could be rusty. Mr Trump refused to participate in the 2024 Republican primary debates, a decision that did him no harm as he easily beat all his rivals for the party's nomination. Mr Biden also has not been on a debate stage in almost four years.
Mr Trump and his team were working ahead of the debate to temper expectations over his performance, arguing - without evidence - that CNN and its moderators, Dana Bash and Jake Tapper, are biased in Mr Biden's favour.
Disinformation danger
Mr Trump is notorious for injecting falsehoods and exaggerated boasts into his remarks, typically requiring a legion of fact-checkers to verify his claims. Mr Biden, too, has been known to tell a few tall tales on the stump.
But there is peril for the opposing candidate in trying to correct the record on stage. "You have limited time," Mr Troy said. "You have to get your points out."
He said fact-checking is a task better left to campaign aides who can quickly send out statements challenging the opponent's assertions.
Many news organisations also will assess the veracity of the candidates' statements.
The narrative trap
There will be a strong temptation for Mr Biden to lean into Mr Trump’s conviction in New York. Mr O’Donnell said that would be a bad idea because it would further Mr Trump’s unsupported contention that Mr Biden was involved in bringing the charges and that Mr Trump is a victim of political persecution.
The Biden campaign recently launched a $50 million ad campaign highlighting Mr Trump's guilty verdict, suggesting the president's team views it as a winning issue. For Mr Trump, the danger lies in saying things that underscore Mr Biden’s argument that he is a threat to democratic norms. Mr Trump, for example, has suggested he will use the Justice Department to target his political enemies.
"Trump has to seem presidential, said Aaron Kall, a University of Michigan expert on presidential debates.
Mr Trump may also be tempted to complain, as he frequently does on social media, about forces working against him or cast himself as a victim of a political conspiracy.
But undecided voters don’t care about Mr Trump’s grievances, Mr O’Donnell said. "Folks aren’t interested in the candidate’s problems, they are interested in their problems."
Political experts said the candidates should emphasise cost-of-living issues - such as high grocery, housing and energy prices - to show they are in touch with voters' sentiments. Mr Biden has been trying to reassure voters about the economy for months with mixed results, and Reuters/Ipsos polls have shown Mr Trump with an edge over Mr Biden as the candidate voters trust to handle the economy.
Democratic pollster Brad Bannon said Mr Biden needs to acknowledge that voters are still having a tough time.
"He must couple his boast of accomplishments with an acknowledgement that consumers still struggle with high prices for gas and groceries," Mr Bannon said.
Mr Biden, he said, "does empathy well. He needs to do much more of it."
No audience feedback
In a sharp departure from previous presidential debates, there will be no studio audience. That could pose problems for both candidates, but perhaps particularly for Mr Trump, who draws energy from a boisterous crowd.
The candidates might be somewhat at sea, getting no real-time feedback as to how their arguments and attacks are being received, Mr Kall said.
With no voters in the room to pander to, the candidates also may be more substantive and less histrionic.
Another danger for Mr Trump: CNN has said a candidate's microphone will be turned off to prevent interruptions when the other is speaking. Mr Trump may decide to try to be heard anyway, risking alienating some viewers in the process.
As a former reality TV star, Mr Trump has deep experience in studio settings while Mr Biden has delivered speeches from the White House without an audience. A key to debate success may be which candidate makes the format work best by connecting viscerally with viewers at home.
Mr Trump will get the final word in the debate, CNN said last week. The Biden campaign won a coin toss to determine podium placement and the order of closing statements, and chose to have Mr Biden on the right side of viewers’ screens during the debate.
The Trump campaign then opted to have Mr Trump deliver the last closing statement.
