7 things to watch at the Kamala Harris-Donald Trump debate

Kamala Harris and Donald Trump's debate in Philadelphia on Tuesday will be a major test – and opportunity – in a presidential campaign that has already been defined by a debate.

Democrats and their progressive allies are fully aware of the stakes after the last head-to-head showdown led to weeks of internal party turmoil culminating in 81-year-old President Joe Biden's dramatic exit from the race.

Many are eager for Harris, known for her resume and reputation as a prosecutor, to take her Republican opponent to task over his unprecedented criminal record and to draw a contrast on critical issues facing the country in front of a national audience.

"What happened in June demonstrates just how important debates still are in a presidential election," said Christina Harvey, executive director of Stand Up America, a liberal-leaning voting rights group.

"It will be important because these two candidates have such a different promise and vision for America's future," she added.

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Former Virginia Gov. Jim Gilmore, who unsuccessfully sought the GOP presidential nomination in 2008 and 2016, agreed that Tuesday's exchange will be "critically important" for both campaigns. But he said it will be far more telling how the Democratic nominee performs under the spotlight.

"My view is that people know almost nothing about Harris," Gilmore said of the incumbent 59-year-old vice president, who previously did run for the White House while serving as a senator from California. "She is going to introduce herself in the debate for the very first time, nobody knows anything about this woman."

Here's a look at what each candidate must emphasize and avoid – and how this debate has the power to sway voters.

With few undecided voters, 'everything matters'

The debate comes at a critical moment in a race that's going to come down to a sliver of voters.

Roughly 90% of likely voters said their minds are "firmly made up," according to a USA TODAY/Suffolk Poll released this month. The survey found about 8% of respondents indicated they might change their mind with approximately 1% saying they are undecided.

"In a close election, everything matters," said Marc Trussler, director of data science at the University of Pennsylvania's program on opinion research and election studies.

Debates don't typically move the needle among partisans, who are the most likely audience to watch Tuesday's broadcast. But even a small number of voters who are skeptical of both candidates might find reasons to choose differently based on this conversation.

"So there's a little bit of persuasion," Trussler said. "Even more so, it's going to be them talking to their bases and trying to build that enthusiasm to vote, something that has been lacking for the Democratic campaign, but has been gaining steadily since Harris has taken over as the nominee."

'Can I call you, Joe?': How Harris and Trump interact

The debate rules are the same as they were in June: no live audience, no props and (over the Harris campaign’s objections) muted microphones when the other candidate is speaking.

But rather than a rematch between two candidates who had tussled for more than four years, this is now an eight-week sprint between two people who've never met in-person. Harris and Trump didn't interact during his State of the Union addresses as president, and he didn't attend her inauguration as VP after refusing to accept the 2020 election results.

Republican consultant Liz Mair, a former spokeswoman for John McCain's 2008 campaign, said the two having no previous interactions could play a role. She said the last time a national debate of this magnitude took place with two candidates who genuinely did not know each other was when then-Alaska Gov. Sarah Palin faced off against then-Delaware Sen. Joe Biden while both were running for vice president.

At the start of that debate in St. Louis, Palin asked: "Can I call you, Joe?" due largely to fumbling his last name throughout her previous preparations. "And that did make a big difference," Mair told USA TODAY.

Political observers will dissect every second of how the two interact in the first few minutes, including how they respond to each other's attacks and the moderators.

Mair said she has guided GOP candidates through debates, and will be watching how Trump responds to Harris, who is the second woman to be a major party's nominee for president after Hillary Clinton led the Democratic ticket in the 2016 race against Trump.

"It's very difficult for male candidates to come off as forceful and authoritative without coming off as being sexist, patronizing (and) condescending," she said. "I think the fact that they haven't met before probably makes that worse."

Ending the Harris honeymoon without offending is Trump's test

Trump and his team have an obvious mission: pop Harris' rising balloon without turning off swing voters who have as many concerns about the former president's character as his policy pursuits.

In the past, the GOP nominee has been known to bring surprise guests to debates and come up with creative insults, but Trump's allies warn against those sort of antics. Instead, he is being urged to focus on the issues that animate conservatives and calling attention to her liberal views rather than vitriolic personal attacks and other ad hominem tangents.

"If Trump stays on the issues, stays on message – and that's by the way can include criticizing Harris for being a flip flopper – that's OK," Gilmore said. "But he needs to then say, 'We don't know what she's going to do, but this is what I'm going to do.' If he talks about the issues, he's going to be fine."

The trouble is Trump isn't always the most disciplined messenger, and often rambles or revels in slinging personal attacks, which have included questioning Harris' racial heritage. At an August event in Asheboro, North Carolina, Trump said people often advise him to be nicer but, "sometimes it’s hard when you're attacked from all ends."

Harris faces danger in debate too, experts warn

For some, the televised debate is more perilous for Harris, who is still introducing herself to a large segment of the country who don't fully grasp what she stands for or will do if elected president.

The VP has reportedly been working on ways to get under Trump's skin by highlighting his repeated false statements while looking for a viral social media moment that could define the race.

But debate experts warn Harris, who remains a relative blank page to voters compared with her Republican rival, faces a steeper fall should a misstep occur that could halt the momentum her campaign has built over several weeks.

"The risk for her is that she's still not that well known to a large portion of the American public, and so it is possible she has a weak performance that she undermines the hope that she's brought to Democrats," said Robert Rowland, a communication studies professor at the University of Kansas.

Harris has done one sit-down interview, joined by running mate Tim Walz, since winning the Democratic nomination. She has been criticized for giving just a handful of policy-focused speeches on the campaign trail and independent voters in particular will be looking for more details.

Harris could be tripped up by Trump or the moderators on why she's changed positions on a number of issues, specifically hydraulic fracturing, commonly referred to as fracking, which is a big issue in the battleground state of Pennsylvania.

In 2019, Harris called for a fracking ban when running for president but told CNN she believes climate change can be tackled without a prohibition on the oil extraction practice.

It will be telling to see how much time Harris spends jousting with Trump versus speaking directly to voters about her plans and views.

'Best decision I made': Biden's record will be as central as the issues

President Biden won't be at this debate, but he's likely to come up for very different reasons Tuesday.

Republicans will want to tag Harris as the true incumbent and anchor her to every controversial decision or bad outcome over the past four years.

Trump has been relentless, for example, in bringing up the botched 2021 evacuation ending the war in Afghanistan that resulted in 13 U.S. troops being killed. He has posted videos online of those soldiers' relatives who specifically blame Harris for the outcome.

In other ads, the Trump campaign calls attention to higher grocery costs with clips of her saying, "Bidenomics is working." That, along with Harris' role in dealing with root causes for the crisis at the southern border and what she knew about Biden's capacity, could all be used against the vice president during Tuesday's debate.

Only 31% of Americans surveyed in the USA TODAY/Suffolk Poll said the country is on the right track versus to 58% who said it is on the wrong track.

As Harris threads the incumbency needle, she might look to defend her boss, who is seeing better numbers since bowing out.

The USA TODAY/Suffolk survey found that about 84% of voters think his decision to drop out was right, and 48% of respondents approve of the job he's doing compared to 41% who said the same in late June.

Other pollsters show Biden's numbers relatively unchanged, but as Democrats and their allies revere the president's choice, any improvement benefits Harris.

"I think that Harris needs to run against Trump, not Biden ... who accomplished a significant amount during his presidency," said Harvey, the voting rights leader.

Harvey said instead of playing defense Harris can go on offense Tuesday by reminding voters about the series of controversies and decisions made during the Trump years. She noted how the next president could make multiple appointments to the Supreme Court in the next term.

Four of the nine justices will be in their 70s by the end of next January, which progressive activists say raises the stakes given the high court's 6-3 conservative tilt.

"They could retire or die or have health issues," Harvey said. "That means that if Trump were reelected, he can ensure MAGA control of the court for decades to come. That would have a huge impact on issues concerning abortion, voting rights and on gun safety."

'Prosecutor v. felon' (or reality TV star)

One thing that infuriated Democrats about the June 27 debate was Biden’s missed opportunity at making a coherent case against Trump on national TV.

Whether it is the Jan. 6, 2021, attack on the U.S. Capitol, handling of the COVID-19 pandemic or his various court cases, Harris comes into Tuesday with an expectation by supporters to put Trump's political and personal record on trial.

The Harris campaign enjoys framing this race as a “prosecutor v. felon.” But a debate stage isn't a courtroom and Trump, a former reality TV star, is experienced in what will be his seventh presidential debate when counting his past White House campaigns in 2016 and 2020.

Debate could break audience records

Biden’s exit, Harris’ entry and Trump's showmanship has given this campaign a cinematic feel that coupled with real world consequences, could make it the most watched presidential debate in U.S. history.

That title is currently held by the 2016 contest between Trump and Hillary Clinton, who drew about 84 million viewers during their first debate.

The other top watched debates are roughly 80 million who watched the 1980 debate between Ronald Reagan and Jimmy Carter; and approximately 73 million who viewed the first 2020 debate between Biden and Trump amid the pandemic.

ABC News will host the event, but if you include other platforms and streaming services this could break records.

This article originally appeared on USA TODAY: Harris-Trump debate: 7 things to watch for at high stakes faceoff