The matchup marked a pivotal moment during the final sprint of a close race for the White House and saw Trump and Harris lay out starkly different visions for the future of America.

While it started with a handshake, the debate quickly saw the Democratic vice-president and Republican former president zero in on each other's records.

Hundreds of supporters gathered for a Democratic watch party at the Dell Music Centre in Philadelphia cheered as Harris said Trump left behind chaos and unemployment at the end of his first administration.

"What we have done is clean up Donald Trump's mess," Harris said.

At a packed watch party organized by Philadelphia Young Republicans at a hotel not far from the National Constitution Centre, where Trump and Harris were on the stage, enthusiastic supporters applauded the former president.

Trump quickly took well-known jabs at Harris, saying, "Everyone knows she's a Marxist." He also criticized the vice-president's record on the economy with the Biden administration.

"She doesn't have a plan. She copied Biden's plan," Trump said.

Republican supporters said they were certain voters could see life was better under the Trump administration.

Tuesday night was a stark difference from the June debate between Trump and President Joe Biden. The previous faceoff saw Trump easily hold his own against a jolting and incoherent Biden.

Supporters at a Democrat-organized watch party in Philadelphia in June seemed disheartened and downcast about their prospects.

The matchup accelerated a cascade of concerns over the president's mental acuity and ability to win the election and led Biden to remove himself from the race.

The tumultuous months between the two presidential debates saw the attempted assassination of the former president, the complete reconfiguration of the Democratic ticket and struggles among Republicans to respond to their new opponent.

Tuesday night watch parties for Republicans and Democrats both were filled with enthusiasm about the outcome of the November election saying their party was making the best case for American voters.

A Pew Research Center survey released Monday suggests the presidential race is deadlocked. It found about half of registered voters -- 49 per cent -- said they would vote for Harris if the election were held today, and an identical share said they would back Trump.

Roneesha Stuart has not decided where her vote may land. She said it felt like Harris was backpedalling on previous stances and making promises she couldn't keep as part of the Biden administration.

"I've been on earth for 32 years and I don't think any president has ever done anything good for me. So I just want to watch. It's entertaining," Stuart said in Philadelphia on Tuesday afternoon.

The Pew report, based on a survey conducted from Aug. 26 to Sept. 2, found Trump's advantage is on the economy, with the majority of voters saying they are very or somewhat confident the former president would make good decisions about economic policy.

Harris leads on abortion and several personal traits, including being a good role model and being honest.

Ahead of the debate, Jahmirah Brown said she believed Harris would stand her ground.

"I feel like my girl is strong," said the 29-year-old from Delaware County, west of Philadelphia.

Harris' debate performance needed to focus on her plan forward and not just reflect on Biden-era policies, said Melissa Haussman, professor emeritus at Carleton University in Ottawa. The vice-president also needed to be clear about her intentions for the economy.

Harris repeatedly said during the debate that she was not Biden, saying, "Let's turn the page."

Haussman said Trump should focus on policy "but I'm guessing he doesn't have the discipline or breadth of knowledge to do so."

The former president often did not answer direct questions and went on different tangents. He made false claims about babies being killed after they are born and repeated unsubstantiated claims that immigrants in Ohio are eating their neighbours' dogs and cats.

But Trump also criticized Harris for changing her policies during her time in office and accused the vice-president of now taking up his proposals.

Neither candidate provided much insight into plans around international trade.

The former president repeated plans for a 10 per cent tariff on imports and threats to not defend NATO members that don't meet defence spending targets, of which Canada is one.

During a NATO leaders' summit in Washington in July, Prime Minister Justin Trudeau promised to meet the spending target, which is the equivalent of two per cent of gross domestic product, by 2032.

Whoever wins the election will be in power during the review of the Canada-United States-Mexico trade pact in 2026.

Many expect Harris will follow the path of her predecessor on Canada-U.S. relations. Harris, however, was one of 10 U.S. senators to vote against the trilateral agreement under Trump, saying it didn't do enough to protect American workers or the environment.

This report by The Canadian Press was first published Sept. 10, 2024.

-- With files from The Associated Press