'What has she done?' Harris must fill in the blanks in high-stakes debate with Trump.

How much do presidential debates matter? The first presidential debate of 2024 changed the entire trajectory of the presidential race, but normally debates aren't that consequential, usually resulting in a net shift of 2 or 3 points in the polls.

However, in a close race such as this year's presidential election, which will turn on a handful of battleground states, even a small shift could alter the outcome.

When one candidate is not well-known, debates can make a difference filling in the picture. Voters know former President Donald Trump well, but they still feel they don’t know that much about Vice President Kamala Harris.

One of the questions we hear frequently about her record as vice president is, “What has she done?” The debate gives her an opportunity to fill in her record, her style of leadership and her toughness.

Debates are the great equalizer when people feel they can compare the leadership and character of the candidates side by side in a neutral environment. Voters judge their style, their treatment of opponents and the way they handle tough questions.

Muted microphones will help Trump in debate

Trump is known to not treat his opponents well – or even civilly – so it is relevant that in this debate, the microphones will be live only for the candidate who is responding to a question, imposing a standard of dignity and composure that might not otherwise be on display.

The muted microphones benefitted Trump in his first debate with President Joe Biden this year, unlike the presidential debates in 2020 and 2016 when Trump constantly interrupted and badgered his opponents to the point where Biden said, “Will you shut up, man?”

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The first debate between Trump and former Secretary of State Hillary Clinton in 2016 was the most-watched presidential debate in history, and while we don’t anticipate the Harris-Trump matchup will approach that level, we do expect more will tune in than watched the earlier debate with Biden.

How much might the Harris-Trump matchup resemble the first Clinton-Trump debate?

Like Harris, Clinton was leading narrowly in the national poll averages ahead of their first debate. She came off as confident and well prepared. When Trump interrupted her, she didn’t appear rattled.

At one point, the debate moderator asked Trump to explain what he meant by an earlier comment that Clinton doesn’t have “the presidential look.” That created an opening for Clinton to itemize the disparaging comments Trump had made about women.

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This year, Trump has said that Harris would be a “play toy” for world leaders, which is something the debate moderators may ask him to elaborate upon. Will Harris exploit it if given a chance, or change the subject as she has done when he has criticized her laugh or racial identity?

Clinton leaned more heavily into gender in 2016, with talk about breaking the glass ceiling and the historic nature of her candidacy. Harris has kept the issue of gender more in the background and is more likely to focus on the issue of abortion rights and individual freedoms.

Voters said Hillary Clinton won debates with Trump

According to the post-debate polls, Clinton was perceived to be the winner of all three debates she had with Trump. And on Election Day, Clinton beat Trump among the two-thirds of voters who said debates were an important factor in their decision, but lost handily to Trump among the 30% who said the debates didn’t play much of a role in their decision.

Debates matter, but they aren’t the only thing that matters. Many people, in fact, will not watch the actual debate but rely on news coverage (or social media) to learn what happened.

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One of the most memorable examples of the impact that media coverage had on perceptions was during the 1976 presidential election between President Gerald Ford and Democratic challenger Jimmy Carter.

After their second debate, voters thought Ford had won and was significantly more likable. By the next morning when the press emphasized that Ford had declared that Poland was not under the control of the Soviet Union, voters shifted to thinking that the president had badly lost, according to internal campaign polling.

What will the news media say about the Harris-Trump debate? Interpretations may vary. We can expect that Fox News won’t show the same clips as MSNBC, so maybe it’s best to tune in for yourself.

Celinda Lake, president of Lake Research Partners, was one of two lead pollsters for Joe Biden's 2020 presidential campaign. She also is a pollster for the Democratic National Committee. Christine Matthews, president of Bellwether Research, is a leading public opinion pollster known for her understanding of swing voters, particularly women.

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This article originally appeared on USA TODAY: How Harris could beat Trump in the debate and still lose the election