And now begins the part of the Quebec election campaign that will decide it all.

After a little more than two weeks that have seen some surprising twists — including the arrival of media mogul Pierre Karl Péladeau as a PQ candidate and champion of Quebec independence — last night's debate represented not only the half-way point in the campaign, but the pop of the starting gun for the race toward the finish line.

Pauline Marois entered the debate with her party trailing in the most recent opinion polls. The PQ has been forced off its original game plan, and Marois has had to address the issue of sovereignty, and whether she would hold another referendum if she forms a majority government. The issue appears to be dragging down PQ support.

Last night, Marois repeated she would not call a referendum "as long as Quebecers aren't ready for one". But she once again refused to categorically close the door to the possibility.

After all, Marois has no choice, since much of her political support base has the firm expectation another referendum be called as soon as possible.

The Liberal leader, Philippe Couillard, came into the debate on top of the polls, but also as the only freshman among the debaters. He was criticized for publicly losing his temper earlier in the week after suggestions of an improper business relationship between himself and the former head of the McGill University Health Centre, Arthur Porter, who is currently being held in a Panamanian prison.

In his first debate, Couillard appeared to deliberately stay cool and calm throughout, even as opponents tried to tie him to the legacy of the last Liberal government that was tossed out of power amid allegations of corruption.

The other two debaters, CAQ leader François Legault and Quebec Solidaire candidate Françoise David, each scored points with viewers through the evening, attacking both Marois and Couillard. But Legault's campaign has stalled in general. And while David was firm and clear throughout the debate, her support base remains very centralized in a small number of Montreal ridings.

What matters in last night's debate is the tone it sets for the critical final two weeks of the campaign.

As was clearly demonstrated by Marois, the PQ will try to turn the focus away from a possible referendum, and stick to two main lines of attack: first, to insist the Secular Charter of Values is needed to ensure the neutrality of the public service; and second, to try tying Couillard to alleged corruption and collusion on the watch of the former Liberal government.

Couillard began the campaign talking about the lagging economy and job creation, insisting only the Liberals have a remedy for both. He will surely continue to do that. But last night revealed he will also keep hammering the PQ on the possibility of a referendum if Marois is re-elected, hoping that will be enough to frighten voters away from giving the Parti Québécois the majority government it is seeking.