ABC News(NEW YORK) — As millions of voters tune in to watch the first presidential debate of the 2016 campaign, there are several key factors to keep in mind.

The general election has been playing out for about two months now, with Donald Trump and Hillary Clinton taking direct aim at one another, but Monday night will be the first time that they square off directly.

Watch the first presidential debate on ABC News and ABCNews.com at 9 p.m. ET. on Monday.

Debate Prep Plays Out on Stage

Clinton has been preparing for her 35th presidential election debate for weeks. Aides say the former secretary of state — who is known for doing her homework — has been poring over briefing books and practicing in mock debates with a Trump stand-in, whose identity has not been confirmed.

Clinton herself has said she expects it to be a “difficult, challenging” debate. Clinton’s campaign has even consulted with The Art of the Deal ghostwriter Tony Schwartz on how to beat him in a debate.

Trump was in debate prep meetings all day Friday after focusing more on campaigning than studying up for the showdown. Though no mock debates occurred, the nominee was asked rounds of possible questions he will face from Monday night’s moderator.

The sessions were led by former New York City mayor and current Trump surrogate Rudy Giuliani along with the campaign leadership.

Testing Their Tones

Acknowledging that there are concerns about his tone, Trump has repeatedly said that he plans to be “respectful” of his competitor, but only to a point.

“I’m going to be very respectful of her,” Trump said during a interview on Fox News on Thursday.

“I think she deserves that and I’m going to be nice. And if she’s respectful of me, that’ll be nice. We’ll have something that I think people will respect as a debate but we’ll see where it all goes. You really never know exactly how it’s going to turn out and that’s why we going to have a lot of people watching,” he said.

For her part, Clinton and her team have spoken about how they had to prep for her to face off against one of two versions of Trump: the more professional, contained version that has been present on the trail more recently or the more bombastic uncontrolled version that was seen more during the primaries.

Famous Faces in the Audience

Chelsea Clinton will attend the debate, a first for her this election cycle after not attending any of the Democratic primary debates.

And another familiar face is expected to be in the front row supporting Team Clinton: Mark Cuban.

The billionaire Dallas Mavericks owner is a vocal Clinton supporter and reportedly went so far as to volunteer to play Trump in Clinton’s mock debates. He said earlier this week that the Clinton team never returned his email offer, but they did keep him in mind for another move.

If Cuban is being put in the front row as some kind of psychological fake-out for Trump, the television audience shouldn’t expect to enjoy his presence. Peter Eyre, a senior adviser with the Commission on Presidential Debates, the independent organization that sponsors the events, told ABC News that the viewing audience will not be in the camera shot during the debate.

All told, there are expected to be about 1,000 people in the viewing audience at Hofstra University Monday night.

The Role of the Moderator

Lester Holt from NBC’s Nightly News has been tasked with moderating Monday night’s debate, and he’s under some pressure.

NBC hosted a Commander in Chief forum during which both candidates fielded questions about their plans for the military, but Holt’s colleague Matt Lauer was widely criticized after the forum for his performance.

Critics complained that he focused more on Clinton’s email scandal than anything to do with the military, and that he let Trump make claims that were false without any intervention.

The question of how much fact checking moderators should do during the debates has been raised. Trump has said that he does not believe the moderators should intervene to fact check, while Clinton raised money off Lauer’s lack of fact checking after the Commander in Chief forum, indicating that she would be in favor of moderators playing a role.

The Spin Efforts Afterwards

While estimated tens of millions of people will be watching the debate in real time, many more are going to be influenced by the social media spin that happens in the aftermath, when the debate about the debate ensues online.

Clinton’s campaign is well aware that the outcome of the debate isn’t just about what the two candidates say on stage, but also about the conversation that takes place around it.

On a conference call with supporters on Friday, a top aide to Clinton directly asked their supporters to use social media during and after the debate to help shape the conversation positively around the Democratic nominee.

The campaign’s digital director Jenna Lowenstein said that two of the campaign’s goals for the night include amplifying Clinton’s best moments online and influencing the narrative about who is winning.

“It’s important that we’re not just turning this into the Donald Trump show,” Lowenstein said.

She instructed: “Tweet early, tweet her name, use those hashtags.”

Watch the first presidential debate Monday at 9 p.m. ET. Full live coverage and analysis of the debate will begin on ABCNews.com/Live at 7 p.m. ET.

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