Philadelphia (AFP) - Donald Trump arrived in Philadelphia for a potentially game-changing televised debate with Kamala Harris Tuesday, the rivals’ first and possibly only clash before November’s knife-edge US presidential election.

The stakes could hardly be higher for the Democratic vice president and Republican former president, with tens of millions of American voters expected to watch them at 9:00 pm Eastern Time (0100 GMT Wednesday).

A single zinger or gaffe during the 90-minute debate could tip the balance of one of the most dramatic White House races in US history, with the candidates neck-and-neck in the polls just 56 days before the November 5 vote.

Trump, 78, touched down in his plane – dubbed Trump Force One – just over two hours ahead of the ABC News-hosted broadcast, while Harris had arrived in the eastern city on Monday.

The pressure is arguably greater for Harris, America’s first female, Black and South Asian vice president, as she takes part in her first presidential debate.

It will be a critical chance to win over voters who still know little about her, as polls showing her honeymoon starting to fade after jumping into the race to replace 81-year-old President Joe Biden in July.

Former reality TV star Trump will attack Harris on issues like the economy and immigration, but may also unleash more of the racist and sexist insults that he’s directed her way during the campaign.

Harris, who enjoys a significant advantage among women according to the polls, is expected to press Trump on reproductive rights after his contradictory comments recently on abortion access.

The debate will be held without an audience, while the rivals’ microphones will only be on when it’s their turn to speak and remain muted otherwise.

- ‘Calm, cool and collected’ -

The last presidential debate in June ended Biden’s election campaign, after he delivered a catastrophic performance against Trump. Harris took over as nominee amid Democratic fears that Biden was too old and too infirm to defeat the scandal-plagued Republican.

Biden told reporters he would watch the debate from New York – where he traveled on Tuesday ahead of ceremonies marking the anniversary of the September 11, 2001 attacks.

“I spoke to the vice president. She seems calm, cool and collected. I think she’s going to do great,” Biden said.

As the tension mounted, Harris did a walk-through of the venue, the National Constitution Center, Tuesday afternoon that lasted about half an hour.

Tim Smith, 39, a Harris supporter, stood outside holding a sign similar to those used by the Trump campaign but bearing the word “Loser.”

Smith said he was hoping “we’ll get to hear a little bit of the policies they want to institute and not so much the name calling or the attacks.”

Inside the venue, both candidates teams were working the “spin room” hours ahead of the debate.

The Democrats brought along two former Trump administration officials who are now harsh critics, including the short-lived White House communications director Anthony Scaramucci.

Harris “will win this debate because she’s going to be focused on issues,” said Scaramucci, who famously survived less than two weeks before being fired in the chaotic Trump White House.

- ‘Lot of untruths’ -

The debate promises to be a bitter battle between two candidates who could hardly have less in common.

In one corner is a former prosecutor who has in the past delivered ice-cold put-downs to debate rivals including Biden himself and Trump’s former vice president Mike Pence.

“There’s no floor for him in terms of how low he will go,” Harris said in a radio interview. “He is probably going to speak a lot of untruths.”

In the other corner is Trump, the most brutal knife-fighter in US politics, who has been convicted of falsifying business records to cover up an affair with an adult film star, found liable for sexual abuse, and is accused of trying to overturn the 2020 election that he lost to Biden.

While many expect him to unleash his usual torrent of outrage and half-truths, he may also opt for a more restrained performance like the one that let Biden self-destruct in June.

“You can’t prepare for President Trump,” his spokesman Jason Miller said. “Imagine like a boxer trying to prepare for Floyd Mayweather, or Muhammad Ali.”