It will be a contrast of styles, political parties, genders, experience and vision for the future when Hillary Clinton and Donald Trump meet at Hofstra University for the first presidential debate here Monday.

No one is sure exactly what to expect — other than fireworks.

And high television ratings.

“They are so different,” said Marist College pollster Lee Miringoff. “They even are going to be talking to two different groups of voters. There’s very little overlap in their base (of support). So a key question isn’t ‘Who can use this to win converts?’ but ‘Who can use this forum to get their people churning?’”

Here are five things experts say to watch for at the first presidential debate:

Insults/flashpoints are likely to dominate.

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In a campaign where the dominant tactic is trying to scare voters about your opponent, each candidate is expected to hold back almost nothing. Will Trump invoke Monica Lewinsky, Gennifer Flowers and other controversies involving ex-President Bill Clinton. What about the Clinton Foundation and its donors? Hillary Clinton emails — is there any doubt?

Conversely, isn’t Clinton going go after Trump’s multiple bankruptcies and business lawsuits? Reports of Trump Foundation money being spent to settle lawsuits against his own company and a portrait of Donald himself? Claims that “Trump University” fleeced students?

The candidates surely are preparing for this. So a question will be how each handles criticism. Trump, especially, unnerved some of his rivals for the Republican nomination with insults.

“In a head-to-head debate, you have to spend of lot of your preparation time anticipating your opponent’s attacks,” said Kevin Madden, a GOP consultant who worked on Republican Mitt Romney’s 2012 presidential campaign.

Clinton should model her approach on the way she handled hours of inquiry about the attacks in Benghazi, said Joel Silberman, a Democratic strategist.

“She was unflappable,” Silberman said. “America needs to see that person: Unflappable. In command of the facts. Strong but not defensive.”

A one-on-one debate demands substance.

Trump was seen as successful in the Republican primary debates by appealing to emotion and tapping into GOP voters’ unrest. With 10 candidates on stage and precious few minutes allotted to each, he avoided giving detailed answers to flesh out many of his promises. That’s much harder to do in a 90-minute, one-on-one format.

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“Hillary is awfully good. She can easily fill the time with details,” said William F. B. O’Reilly, a Republican consultant. “If he tries to go toe-to-toe with her on policy, he will be diminished.”

His biggest promise was to “build a beautiful wall” along the U.S. southern border and force Mexico to pay for it. But Mexico’s President Enrique Pena Nieto already has said he won’t. Trump has said he has a plan to destroy ISIS, bring back jobs from overseas and renegotiate trade deals. But he’s has not explained how he could accomplish any of these.

Similarly, Clinton sought to woo backers of Sen. Bernie Sanders (her main rival for the Democratic nomination) by adopting his proposal for free public colleges. She’s modified it slightly but hasn’t explained how to cover the costs. Sanders vowed to dramatically hike taxes on Wall Street companies and other corporations. Clinton hasn’t spelled out her plan.

Trump ad-libbing or “on message”?

Trump has said he doesn’t like to prepare too much for debates and TV appearances, saying that doing so can make a person seem scripted. But O’Reilly noted that Trump’s recent surge in the polls occurred when he began using a teleprompter at rallies and “staying on message” instead of just free wheeling.

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“The entire question may be can he stay disciplined without a teleprompter,” O’Reilly said. “If he can’t, he may lose the momentum he’s gained recently.”

Body language counts.

Checking your watch. Sighing. Pointing your finger. Leaving your lectern.

Campaigns are filled with seemingly small gestures that often become the most remembered moments of debates. That’s why everything from the placement of the lecterns to use of your hands to facial gestures are critically important in a televised debate, according to Jack Brown, a body language expert who has been blogging about candidates.

Some of Brown’s critiques: Trump points too much at the audience and too often shows his palms to the audience (Great for solidifying your base an intraparty skirmish, but not inviting to undecided voters or non-hard core supporters).

Clinton, he says, turns her body toward the opponent too much (Gives your foe the entire audience) and leans back too much (conveys “looking down your nose” — something she never did during the Benghazi hearings, Brown notes).

Some advice: Always point your body at directly at the audience (or in this case, TV cameras), not your opponent. Don’t look down (looks like being reprimanded) unless taking notes. Don’t point, but use gestures such as holding an invisible basketball (denotes inclusiveness). Use metaphors (makes you more open to the audience). Don’t leave the lectern — recall the 2000 New York Senate campaign when Republican Rick Lazio walked over to Clinton to demand she sign a campaign pledge, a move that backfired completely.

Moderator’s control.

Throughout the Republican primary debates, Trump and other candidates often verbally trampled over the moderators, ignoring questions, trying to outshout one another and struggling for a few precious minutes of airtime. That was in large part because 10 candidates were on the stage at once.

(The Democratic battle, which quickly whittled down to Clinton and Sanders, didn’t have the same issues.)

So a key question is how well will NBC’s Lester Holt try to direct and control the conversation?

Trump, using a tactic employed by sports coaches, has begun trying to “soften up the referee” by complaining ahead of time that Holt won’t be fair to him. Clinton allies have said Holt must hold Trump accountable for the truthfulness of his statements.