When Hillary Clinton and Donald Trump take to the stage at Hofstra University in New York on September 26, they will make presidential debate history for not just one, but for several reasons.

It will be the first time that a female candidate is featured in a US presidential debate. It will be the first time that the two most unpopular presidential candidates share the stage at the same time for a one-on-one faceoff. And it will mark the first time for Donald Trump to appear in a presidential debate not against several, but only against one opponent.

"The stakes are very very high for both of them going into this first debate," said Reed Galen, a Republican political strategist who has worked on the presidential campaigns of George W. Bush and John McCain.

Robert Shrum, a Democratic political consultant who worked on the presidential campaigns of Al Gore and John Kerry agrees.

"I think they are critical," he said, adding that because of international concerns about Republican presidential candidate Donald Trump, "they will worldwide be the most-watched television event since the moon landing."

Wild card

The most intriguing question ahead of the first debate is which Donald Trump will show up.

"The biggest wild card of all is what Donald Trump is going to do," said Galen. "Will Donald Trump try to be a more traditional politician where he makes a point about specific issues or is he going to come out and just do what he did in the Republican debates - which is say crazy things that totally obscure where he stands on any given issue."

Simply "winging it," agree the experts, as Trump's strategy has been described repeatedly, is not going to be sufficient in the presidential debate. During the Republican primary debates Trump sometimes shared the stage with 10 other candidates. Consequently each candidate had comparatively little time to speak and develop concrete policy ideas. Among a pool of many widely unknown candidates, to dominate the debate and create a lasting impression was essential - a task Trump clearly excelled at.

To succeed in an uninterrupted two-way presidential debate lasting 90 minutes will be a whole different ballgame for Trump, said Jennifer Mercieca, a political rhetoric scholar at Texas A&M University who studied the candidates' primary debates and their performance at the more recent commander-in-chief forum.

Policy knowledge

"I think this will be an occasion where he will need policy," she said. That's because in his previous debates, Mercieca explained, Trump had only one minute for a response, but still struggled to come up with substantive things. In the upcoming presidential debate Clinton and Trump will each have two minutes for responses.

"The two-minute response is actually a long time for Donald Trump," said Mercieca.

In the presidential debates, predicted Galen, Trump's mainstay rhetorical tactics, namely "dissembling and attacking," won't suffice anymore. "Dissembling," i.e. talking about something unrelated until he knows his time is up, and "attacking," i.e. going after the moderator for a question he perceives to be unfavorable to him, will score points with ardent Trump supporters, conceded Galen. But they will do little to persuade the crucial group of undecided voters that both candidates need to reach, he added.

Due to his previous performances Trump has a low bar to cross, said Galen, "because everybody expects that he is going to go onstage and basically throw the podium into the audience." Despite those low expectations, Trump still has to do more than just avoid outrageous remarks, argued Galen, because the American people expect from a presidential candidate not only that he or she knows how the world and the country work, but that they offer concrete plans on how to fix America's problems.

"The question is whether Donald Trump can even begin to illustrate how he would do that," said Galen.

"Trump has to pass the threshold of acceptability and at the same time show genuine knowledge and mastery of the substantive issues," said Shrum. "He has generally gotten away with not having that."

Trustworthiness and honesty

Compared to Trump, the format and the policy issues debated should come fairly easily for Hillary Clinton, noted the experts. That's because Clinton, since her first run for the US Senate in 2000, has participated in many similar events, most recently in the Democratic primary against Bernie Sanders. Clinton also has such a good grasp of all relevant policy issues, said the experts, that she must watch out not to come across as too wonky.

"The difficulty for Clinton is that she tends to over-explain," said Mercieca. "She may come off as too calculated or too rehearsed in such a way that it makes her seem untrustworthy and potentially unlikeable as a leader."

The debate is crucial for Clinton because polls have tightened and questions surrounding her trustworthiness and Fitness have only grown louder recently. That's why her key challenge in the debate will have little to do with whether she performs adequately, but rather with her "own trust issues," as Galen put it. Polls have shown that Clinton, like Trump, is deemed not honest and trustworthy by large swaths of the US electorate.

While the deep-seated perception that Clinton is not trustworthy may be impossible to shake in the debates, she will nevertheless try to present herself as the stable, logical and safe option in this race, a leader who has the experience and the temperament to become president, predicted Galen: "Whether anybody believes that is another story. But that is the image she is trying to project."

Gender issue

Galen also expects Clinton to use the debate as an opportunity to back off from her controversial remark that half of Trump's supporters could be put into a "basket of deplorables." "But she will also make it a very salient point to remind those Latino and those African-American voters that this is a guy who does not like you. And he has got a lot of people behind him who really don't like you," he added, referring to the disparaging remarks Trump made about both groups.

Given Donald Trump's controversial treatment of women like Fox News presenter Megyn Kelly and Republican presidential contender Carly Fiorina during the course of the campaign, the gender dynamic between Trump and Clinton - the first female presidential candidate - will be another key thing to watch for, said Mercieca.

"Typically Americans would not like to see a man be aggressive to a woman in a debate," she noted, "but I think that Trump supporters would love to see him be aggressive toward her."

"I'm not sure how it would play out with undecided voters. I would think that it would add to the view that he is a misogynist and, like the incidents with Megyn Kelly and Carly Fiorina, I think that it could make him look less than presidential."

Asked for their predictions of how the first debate would turn out, none of the experts ventured a guess. Instead, their advice was to simply wait and see whether Donald Trump has something up his sleeve on September 26.