"Harris going in had the most to gain and also the most to lose," said Allison Prasch, an expert on U.S. presidential rhetoric at the University of Wisconsin.

"I think she came in and really delivered an effective debate performance."

Tuesday's matchup saw Harris push the former president on his record and bait him into tirades far from Trump's intended goals of focusing on immigration and the economy.

The former president's strategy is always to dominate the discussion and the stage, said former Republican strategist Chip Felkel. Harris was able to rattle Trump, Felkel added, and put her courtroom experience on display.

"I think for the first time in his political life since 2015 somebody figured out how to push back," Felkel said. "Not only to push back, but to dominate."

Trump criticized Harris's record, and her changing stance on issues like fracking and immigration.

Prasch said Trump's most effective criticism came during his closing argument, when he criticized Harris for not being able to achieve her current election promises in the more than three years she's been vice-president with the Biden administration. At that point, Prasch said, it was likely too little, too late.

Harris stayed focused and gave clear answers throughout the more than 90-minute debate. She also used her face and body to demonstrate when she thought statements from Trump were absurd or wrong, including the former president's unsubstantiated claims that immigrants in Ohio are eating their neighbours' dogs and cats.

"I think she gave a killer performance," said Saleena Temple, who attended a Democrat-organized watch party.

"I appreciate how she addressed him and put him in his place but in a tactful manner, a professional manner, a political manner. She looked presidential."

While Trump said he thought it was his best debate performance, Harris was rewarded at the end of the night with an endorsement from pop juggernaut Taylor Swift.

At a watch party a few blocks from where the debate was taking place, Matthew Lamorgese, chairman of the Philadelphia Young Republicans, said he believes voters know they can count on Trump's record.

"Under Donald Trump, we had a strong economy, low inflation, and a secure border," Lamorgese said. "We had world peace .... That's what you are going to see."

Experts say Harris has proven a problematic opponent for Trump so far on the campaign trail. Lamorgese said he wasn't worried about the vice-president's performance against the Republican former president.

"Kamala has a different set of issues but issues nonetheless," Lamorgese said.

Tuesday's debate was a stark contrast to the first presidential debate in June, where Trump easily dominated an unclear and uneasy performance by Joe Biden, which ultimately led to the president dropping from the race.

The race for the White House remains razor thin after a tumultuous summer that has included an assassination attempt of the former president and a wholly reimagined Democratic ticket.

Experts say many would-be voters are just starting to tune in to the campaigns.

Pennsylvania, where the debate took place, has become the forefront battleground state where both parties are trying to gain favour. Trump took it in 2016 before it swung back to Biden in 2020 -- both by narrow margins.

Matthew Lebo, a specialist in U.S. politics at Western University in London, Ont., said Harris may see a bump in approval after the debate but she still has a lot of work to do ensuring voters know her policies and personality ahead of November.

The debate was light on policy particulars. Trump continued his threats to not defend NATO members that don't meet the alliance's defence spending targets, of which Canada is one.

Prime Minister Justin Trudeau promised in July to meet the spending target, which is the equivalent of two per cent of gross domestic product, by 2032.

Harris talked about America's ongoing support for the defence alliance and criticized Trump's relationship with Vladimir Putin and close ties to Hungarian Prime Minister Viktor Orban.

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

Harris 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.

Trump repeated his plans to increase tariffs on imports and Harris spoke about ensuring American jobs remain in the U.S.

"Tariffs would certainly hurt trade with Canada if he ever went through with that," Lebo said.

Canadians should be most concerned about Trump's continued denials of responsibility for any role in the Jan. 6 attack on Capitol Hill and what that means for democracy, Lebo said.

"That's just dangerous and Canadians, on the border of the United States, need a stable democracy there," Lebo said.

"And he's just undermining that."

This report by The Canadian Press was first published Sept. 11, 2024.

-- With files from The Associated Press