NOTE: NBC Chicago will broadcast the debate live once it begins at 8 p.m. CT. Watch here.

While many focus on the word choice during Tuesday night’s presidential debate between Vice President Kamala Harris and former President Donald Trump, another element is quietly emerging that could play a major role.

Body language.

Of course, there will be a clear gender dynamic on stage on Tuesday night.

The candidates, who have never met in person, are expected to stay behind their lecterns, but Republicans are hoping Trump will avoid further provocations, such as pointing fingers at Harris, yelling at her or addressing her in other ways that could alienate suburban women or other swing voters.

Harris, too, will face unique challenges related to her race and gender as voters consider whether to make her the country’s first female president. Some voters still say they are uncomfortable with the idea. If she comes across as angry, she risks perpetuating racist stereotypes about black women.

From her early campaigns in California to her time as President Joe Biden’s vice presidential candidate, Harris has developed an aggressive yet balanced approach to the debates.

She tries to mix punchlines with details that build a larger narrative. For example, she shakes her head to express disapproval as her opponent speaks, counting on viewers to see her reaction on a split screen.

And she has a tried-and-tested tactic for turning debates back in her favor: She says she likes to answer a question while gathering her thoughts to explain a developing point or defend an earlier one.

It would not be the first time that Trump has debated a candidate who wants to become the first female president of the United States.

As Trump and Harris prepare for their first – and possibly only – debate, his three meetings with Clinton in 2016 underscore the challenges facing both candidates in what is shaping up to be another extremely close election.

Harris will face a skilled and experienced debater who knows how to unnerve his rivals with a barrage of insults and interruptions while exuding unwavering confidence and conviction.

And Trump will be dealing with a prosecutor who has many years of experience and is known for his targeted strikes.

While gender dynamics play a role, don’t underestimate the importance of the age difference.

Harris is nearly two decades younger than the 78-year-old Trump. Age was seen as a political advantage for Trump when he ran against the 81-year-old Biden, but now the opposite is true when it comes to the 59-year-old Harris. If he wins, Trump would be the oldest US president ever elected.

When you ask Trump’s former debate opponents what they are paying attention to on Tuesday night, many say the same thing: They are looking for the things he says or does that Harris cannot possibly prepare for.

Trump is the ultimate wild card, having achieved enormous political success by ignoring the traditional rules of politics. He will say or do whatever he thinks is best at the moment. And Harris, who has devoted several days to debate preparation, cannot plan for everything.

Trump’s own team doesn’t know what he will do or say on any given day. That’s incredibly risky for Trump. But it also puts enormous pressure on Harris.

According to Donald Trump’s campaign team, his unpredictability will give him a decisive advantage in Tuesday’s debate.

“You can’t prepare for President Trump. You just can’t,” said Jason Miller, the senior campaign adviser, in a phone call with reporters on Monday. He compared the challenge for Vice President Kamala Harris to “a boxer trying to prepare for Floyd Mayweather or Muhammad Ali.”

“You just don’t know what angle they’re coming at you from,” he said.

Still, his advisers say, Trump will focus on linking Harris to the Biden administration’s most unpopular policies. Trump will try to blame her not only for border, inflation and foreign policy decisions, but also for other things that happened during her tenure, such as the devastating Maui fire last year.

“Kamala Harris owns everything in this administration,” Miller said.

Former Rep. Tulsi Gabbard, who ran against Harris in the 2020 Democratic primary and helped Trump prepare, said his tone would not change this time, even if he was facing a woman.

“President Trump respects women and doesn’t feel the need to be condescending or talk to women differently than he would talk to men,” she said. “So he’s speaking to the American people, he’s talking about Kamala Harris’ record and comparing and contrasting that with his record.”