Two old rivals, who have spent much of their political lives duelling over the issue of Quebec independence, held Monday what might have been their final dance.

Jean Charest and Pauline Marois concluded a one-on-one televised debate with an exchange that could have taken place at any time over the nearly 15 years that the two have faced each other in the Quebec legislature.

The Liberal premier accused her of fostering instability, with her talk of independence. He demanded that she come clean and tell Quebecers whether she would hold a referendum.

The Parti Québécois leader, the current election front-runner, was vague in her answer. There will be a third plebiscite on independence, Marois suggested, whenever the PQ feels it can win.

"A referendum if necessary, at the moment it's necessary," Marois said.

But she reassured voters not to worry when casting their ballots on Sept. 4, because a PQ government would prepare the province for a referendum well in advance by repeatedly making its case for independence: "We won't have a referendum in secret."

With a bite in his tone Charest, fighting for his political survival, was more combative than usual Monday. He accused Marois of "discrimination" with a proposed law that would restrict religious headwear in public spaces and force public office-holders to speak French.

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Charest had a wry answer after the debate when asked whether he was angry at Marois. (Paul Chiasson/Canadian Press)

And he said her ever-present referendum threat would lead to instability.

"(She) will place a sword of Damocles over Quebec's society and economy by saying, 'I'll hold a referendum when it suits me,"' Charest said.

"The last thing we need is referendum threats... You're gambling at the casino with Quebec's future."

Charest was asked by a reporter after the debate whether he was angry at the PQ leader. Charest replied, dryly: "No more than usual." Marois later told reporters that she found her rival "very aggressive."

With two weeks left in the campaign, there is a strong chance that only one of Monday's two debate participants will continue in provincial politics after the Sept. 4 election.

If so, this was their final face-to-face campaign debate.

Over the next two nights, under a unique debate format being used in the current Quebec election, both Marois and Charest will square off in one-on-one encounters against a new foe: Francois Legault.

Legault, the leader of the fledgling Coalition party, has no official position on the independence question and promises not to discuss the issue that has dominated Quebec politics since the late 1960s.

'The last thing we need is referendum threats... You're gambling at the casino with Quebec's future.'—Jean Charest, Quebec Liberal leader

The next two debates could be pivotal.

Legault's party is challenging both of the older ones for votes, and the impressions left after Tuesday and Wednesday's events could hold a ripple effect on the three-way race.

4 debates in 4 nights

Monday's event, the second of four debates in four nights, featured the following topics: governance, social policy, the economy and the national question.

The issue of student strikes, which had fallen off the radar during the Quebec election campaign after captivating the province for months, made a brief return as an election issue.

The tuition dispute has been a non-factor in recent days as students have massively voted to return to class. The issue, which was making international headlines just a few months ago, didn't even come up in the first leaders' debate Sunday.

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Charest trades words with Marois as TVA's Pierre Bruneau moderates in Monday night's one-on-one debate. (Courtesy TVA)

But it was raised in the second debate, in a question from the moderator Monday.

Marois was asked to clarify her position on the tuition hikes. She replied that, yes, she was against the $254-a-year increases. Marois has already said her government would call a summit with students and propose indexing tuition increases to the rate of inflation.

That earned her a scolding from the Liberal premier.

"I will not bend to the street like you did," Charest said. "Sometimes, governments need to make difficult decisions... Otherwise, Quebec becomes ungovernable."

Marois pointed out that only a tiny minority of protesters last spring actually participated in vandalism. She said most were peaceful, and the premier could have encouraged social stability by sitting down with them sooner and listening to their concerns.

"You divided Quebecers," Marois said.

"I believe a head of state has some responsibility in that regard."

Ethics a hot topic

Monday's event began with the subject that has caused Charest the most problems: ethics scandals. He sought to neutralize that issue by launching a counter-attack on the ethics of his rival.

For a moment, Charest and Marois were engaged in an exchange of insults over who was most to blame for crooked political fundraising.

Charest said Marois' PQ had no right to claim the moral high ground on the issue. He said his rival's 2007 leadership campaign had received more than three-quarters of its funding from people tied to firms in the construction industry.

He also raised a $2,500 donation to Marois from a teenager, and a 2006 report that suggested the notorious Groupaction marketing firm had illegally donated almost $100,000 to the PQ while it was in power.

'It's not you who is going to give me lessons on integrity, Mr. Charest.'—Pauline Marois, PQ leader

Charest said he was tired of having his party's reputation besmirched for two years, and of seeing the entire political system fall into disrepute.

"Many unfounded allegations were made," the Liberal premier said.

"The political class has some responsibility for that — including Madame Marois."

Marois shrugged off his attack. She listed some of the controversies to rock the Liberals. They included a minister having a fundraising meal with a reputed member of the Mafia, as well as lucrative government contracts going to Liberal party donors.

"It's not you who is going to give me lessons on integrity, Mr. Charest," Marois replied. "It's indecent."

She said her PQ would go farther than Charest has in tightening political fundraising laws, and reiterated her promise to lower the donation limit to $100.

Charest has introduced a series of laws with respect to public-works contracts, political fundraising, and has created police squads that have already made numerous arrests.

The province is experimenting with an unconventional debate format in the runup to the Sept. 4 election. Three of the four encounters will see one-on-one contests, rather than all four main party leaders on stage at the same time.

After Monday's event there will be another small debate Tuesday, involving Charest and Legault, leader of the new Coalition party. Then finally Legault and Marois, who are former cabinet colleagues, will face off against each other Wednesday.

The only debate featuring all the main party leaders on the same stage occurred Sunday night. Marois used Sunday's event to repeatedly attack Prime Minister Stephen Harper, in a hint of federal-provincial battles that might follow the Sept. 4 vote.