Donald Trump and Kamala Harris are preparing to meet for the first time in Pennsylvania in their only scheduled debate of the US presidential campaign, a key moment in a close-fought contest.
The nationally televised debate on ABC News, beginning at 9pm eastern time (2am Irish time) takes place just eight weeks before the 5 November election, and days before early voting will start in some states.
Former president Trump said he would contrast the left-wing policies Ms Harris proposed in her failed 2020 presidential bid with the more centrist positions she has staked out now.
"You don't know what to expect. She's changed all of her policies over the years," he told NBC News in a phone interview.
Vice President Harris indicated she will draw attention to Mr Trump's habit of lying.
"Donald Trump has a real problem with the truth," she wrote in a social media post this morning. Her campaign released an ad featuring former US president Barack Obama ridiculing Mr Trump's false claims about crowd sizes at his events.
Ms Harris will also talk about her plans to lower Americans' daily expenses, campaign advisers said.
The encounter is particularly important for Ms Harris, with opinion polls showing that more than a quarter of likely voters feel they do not yet know enough about her.
The debate offers Ms Harris, a former prosecutor, a chance to make her case against Mr Trump, whose felony convictions, outspoken backing for supporters convicted in the 6 Januuary 2021, attack on the US Capitol and frequent falsehoods offer plenty of fertile ground.
First meeting
It will be the first time the two candidates have met and follows weeks of personal attacks on Ms Harris by Mr Trump and his allies that have included racist and sexist insults.
Mr Trump's advisers and fellow Republicans have urged him to focus on the high levels of inflation and immigration that have taken place during Democrat Joe Biden's presidency, though both have dropped dramatically this year.
"He's ready to talk about why your life was better when he was in office," Lara Trump, the candidate's daughter-in-law, said on CNN.
Presidential debates do not necessarily change voters' minds, but they can transform the dynamics of a race. Mr Biden's performance against Mr Trump in June was so damaging that it eventually led him to abandon his campaign.
In a contest that could again come down to tens of thousands of votes in a handful of states, even a small shift in public opinion could alter the outcome.
The two candidates are effectively tied in the seven battleground states likely to decide the election, according to polling averages compiled by the New York Times.
"There is more for Kamala Harris to gain and more for her to lose," since she remains less known to many voters, said Mitchell McKinney, a former adviser to the US Commission on Presidential Debates.
Viewers will be looking for where she stands on various issues. But just as important, they will be looking to see how she handles herself against Mr Trump, who is already well known.
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Muted microphones
The 90-minute debate, hosted by ABC News, will take place at the National Constitution Center in Philadelphia. As agreed by the campaigns, there will be no live audience and microphones will be muted when it is not a candidate's turn to speak.
Ms Harris has been preparing in Pittsburgh since last Thursday, holding mock sessions on a stage with lights to recreate the debate environment.
Mr Trump has relied on informal chats with advisers, campaign appearances and media interviews to prepare, with former Democratic congresswoman Tulsi Gabbard - who had a memorably hostile exchange with Ms Harris in a Democratic presidential debate in 2019 - offering advice.
On a call with reporters, Ms Gabbard said Mr Trump would treat Ms Harris the same as any other opponent.
"President Trump respects women and doesn't feel the need to be patronising or to speak to women in any other way than he would speak to a man," she said.
Voters in Philadelphia on what they expect ahead of the Harris and Trump debate
While any personal crossfire will get plenty of attention, the two rivals are also likely to skirmish over issues.
Abortion has been a top issue for Ms Harris and Democrats since 2022, when the US Supreme Court - powered by three Trump appointees - eliminated a nationwide right to the procedure in a broadly unpopular decision.
Ms Harris has also sought to tie Mr Trump to Project 2025, a conservative policy blueprint that proposes expanding executive power, eliminating environmental regulations and making it illegal to ship abortion pills across state lines, among other right-wing goals.
Mr Trump has offered shifting rhetoric on abortion while distancing himself from Project 2025, even though many of his former advisers were involved in the effort.
Mr Trump is expected to highlight Ms Harris' past support - since disavowed - for left-wing stances such as banning fracking, portraying her either as a flip-flopper or an extreme liberal in disguise.
A recent New York Times/Siena poll found that Mr Trump is leading Ms Harris nationally by 48% to 47%, well within the margin of error.
An ABC News/Ipsos poll showed Ms Harris leading Mr Trump 50% to 46%.
The ABC News Presidential Debate will be broadcast live at 2am tomorrow (Irish time) on the RTÉ News channel.
