08/06/2015 06:53 EDT | Updated 08/06/2016 05:59 EDT

Maclean's Debate: These 5 Things Are Crucial To The Leaders' Performances

OTTAWA — Here are five things to watch for in tonight's leaders' debate.

1. Delivery: Of course, the substance of the discussion matters. But debate experts say the way messages are delivered matters most. For political leaders, the greatest challenge will be to relay key points — be it on the economy, security or the environment —because viewers can only retain a certain amount of information. The four leaders all have a big microphone tonight, so they have to be selective about the messages they leave with their audience.

2. Appearance: The way political leaders hold themselves sends a strong message, and yes, it is a superficial one. NDP Leader Tom Mulcair appeared at a press conference ahead of the debate wearing a sharp black blazer, a crisp white collared shirt and no tie. His body language was more relaxed than in days prior; on Day 1 of the campaign, political observers described Mulcair as rigid and uncomfortable. All four leaders will have to appear confident and professional under the gun. But they'll also want to come across as approachable to Canadians.

3. Speech writing: Maclean's magazine has not revealed all of the details on the structure of the debate, but leaders have been rehearsing key lines behind the scenes with members of their inner circles. Writers have also been working for months to arm their bosses with strong jabs and policy statements that will work as sound bites — clips that make their way into the news coverage, helping to propagate the party's message. In the end, it's all about branding.

4. Strengths: Each leader has their strengths. Conservative Leader Stephen Harper brings a great degree of experience to the table; as a result, he'll be expected to remain calm under pressure. Conrad Winn, a political science professor at Carleton University in Ottawa, says Harper isn't the one to watch because viewers know what to expect from him. Winn says the debate is really about what's at stake for the opposition leaders, who are all jockeying for more support. 

5. Vulnerabilities: Each leader also has weak spots. Liberal Leader Justin Trudeau has come under fire from his opponents for his lack of experience. Trudeau's team obviously knows he has to counter that narrative; the debate offers a good opportunity to turn the tables. Conservative spokesman Kory Teneycke said he anticipates Trudeau has memorized lines. The Liberal leader's rivals will be looking to put him in the hot seat in hopes of watching him crack under pressure.

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