The grill marks that NDP Leader Tom Muclair tried to leave on Essex MP Jeff Watson this week are one more indication that things are heating up on the pre-election trail this summer.

Mulcair stuck the prongs in Watson, during a stop in the Conservative MP's hometown of Amherstburg, Ont., on Thursday, accusing him of being a "servile follower" of instructions from the Prime Minister's Office.

Laura Stephenson, an associate professor in the department of political science at Western University, said she had been expecting the federal leaders to spend their summer building goodwill on the barbecue circuit.

But Mulcair's recent message to Watson suggests that the NDP leader won't simply be posing for photographs and shaking hands in a bid to shore up support from voters in the weeks ahead.

"I think the NDP has chosen to make a stronger effort, or at least it appears to be from where I'm sitting, to not be as casual about it and be a little more pointed about it and it seems wise to me," she told CBC News in a telephone interview from London, Ont., on Friday.

Ian Capstick, a political commentator and managing partner at Media Style, an Ottawa-based communications firm, said that it's clear the campaign has already begun.

"The campaign is for all intents and purposes on," said Capstick, who is a New Democratic Party member, but is not officially involved in any campaign work.

He said the public can expect the New Democrats and the Liberals to continue pushing the Conservatives on their record, including that of their elected members "who have not been able to deliver some of the promises that perhaps brought them into office in the first place."

'They are going to use every tool they have'

Given that the Conservatives are known to be strong campaigners, Stephenson said it seems clear that the New Democrats know what they are up against and have opted for a pragmatic approach to taking them on.

She expects that approach won't be limited to remarks from the leader, either.

"I think that the NDP is going to hit hard and they're going to say, 'Listen, you don't want them, they haven't done it for you' and they are going to use every tool they have to get that message across to voters," said Stephenson, pointing to an attack ad the New Democrats released this month, which has been watched more than 500,000 times.

Stephenson said the public shouldn't expect anything different from the Conservatives.

The ideological divide between the parties feeds the style of attacks that these parties use on one another.

"These two parties are on opposite ends of the spectrum for Canada and that makes a difference," Stephenson said, speaking of the New Democrats and the Conservatives.

By contrast, Stephenson said the Liberals have a greater challenge in refining their attacks, given the overlap they may have with either the Conservatives or New Democrats on selected issues.

"When it comes to the NDP, I mean, on most issues, they are far apart from the Conservatives, so for them to say, 'Look, they've done a poor job, we don't like them, we don't like what they're doing, you don't want them,' they can be pretty steady on that line of argumentation," Stephenson said.

Stephenson said the fact that an election is no further than 90 days away means the parties can plan ahead.

"They know that the election won't be later than a certain date and so it makes sense to try and get their ducks in a row early," she said. "And so, for each party, I think it's a huge strategy that they've put in place of what they're going to say when and what they're going to emphasize at what point."

Capstick said the fixed election date has had the effect of creating the "longest campaign in Canadian history."