Trump-Harris debate live updates: Candidates spar over Project 2025, economy

Tonight's debate marks a rare historical moment in that it pits against each other two candidates with significant track records in the White House.

That "political baggage" can be a curse for the candidates, according to experts who've studied debates, but also a blessing, depending on how it's portrayed and defended.

Both Harris and Trump will need to walk a fine line between affirming what they consider their successes during their administrations, experts said.

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-ABC News' Ivan Pereira

Debates are a rare opportunity for candidates to change their perception among the American people. And right now, Harris is perceived more positively than Trump. According to 538's polling average, 46 percent of Americans view her favorably, while 47 percent view her unfavorably. While that's not exactly popular, it's a remarkable reversal from just a couple months ago. Before Biden dropped out of the presidential race, Harris had a net favorability rating of -16 points. But since she kicked off her campaign, her favorable rating has shot up, while her unfavorable rating has plummeted.

By contrast, according to 538's polling average, 43% of Americans view Trump favorably, while 53% view him unfavorably. Those numbers have been pretty consistent over the years. Trump's unfavorable rating has been about 10-15 points higher than his favorable rating since he left office in 2021, and his average job approval rating was in the same range for most of his term as president.

—538's Nathaniel Rakich

As speculation mounts over how Trump will go after Harris -- on policy or personality -- Sen. Rick Scott, R-Fla., a top Senate ally, insisted the former president will stick to issues Americans care about.

"He's going to do great," Scott told reporters in the spin room in Philadelphia. "He's going to talk about the issues."

-ABC News' Tal Axelrod

The stakes for this debate are high for both candidates for one very simple reason: The presidential race is extremely close right now. In some of the states most likely to decide the election — such as Pennsylvania, Georgia and North Carolina — 538's polling averages show Harris and Trump within 1 percentage point of each other.

Nationally, Harris leads Trump by an average of almost 3 points, raising the possibility that she could win the popular vote but lose the Electoral College, as Hillary Clinton did in 2016. According to 538's average, Harris's national lead peaked at 3.7 points on Aug. 23, the day after the Democratic National Convention, but her advantage has slipped a bit in the weeks since.

-538's Nathaniel Rakich