The French-language debate that took place Thursday night could not have come at a more important time for the New Democrats. With their lead shrinking in Quebec, and costing them their nationwide edge, leader Tom Mulcair needed to bolster his support among francophone Quebecers.

The CBC Poll Tracker now gives the Conservatives a small lead in the polls, with 31.3 per cent support against 30.3 per cent for the Liberals and 28.9 per cent for the New Democrats. This marks the high-water mark for the Tories so far in this campaign and the lowest average score for the NDP since the end of May.

The decline for the New Democrats has been slow but consistent. The party was averaging about 32 per cent in the Poll Tracker from Sept. 2 to 13, but it has since dropped steadily. Both the Liberals and Conservatives have seen their support levels marginally improve in the meantime

Polls were in some disagreement Thursday, with Nanos and Léger showing the same three-way race and EKOS recording a wide lead for the Conservatives. But the bulk of the evidence (both polls from Nanos and Léger contain newer data than does EKOS) points toward the same close contest that has defined the campaign for the past few weeks.

However, with the race so close among the three parties, these numbers could easily reverse themselves without requiring any dramatic movement. Even the trends that seem to be building could prove ephemeral.

NDP in front, but down, in Quebec

Where there is a clear movement in the polls is in Quebec. The Poll Tracker currently pegs the NDP to have the support of 38.9 per cent of Quebecers, down almost 10 points from where the New Democrats stood on Sept. 9 and alone enough to have cost the NDP the lead in national polls. The Liberals follow in second with 23.9 per cent while the Conservatives and Bloc Québécois trail with 17.8 per cent and 15.6 per cent, respectively. All three parties have seen their numbers improve as the NDP's have dropped.

At stake for the leaders in the French language debate:

The polls have been consistent in this regard. Five of the last six polls in the province have put the NDP below 40 per cent while 30 of the previous 34 surveys had them over that mark.

The New Democrats still retain some important advantages in Quebec, however. Their lead among francophones is still wide and can deliver them a large number of seats.

The party's overall lead in the province is hardly in danger yet, but the 51 to 58 seats the NDP would likely win with its current levels of support do not match the 59 the party took in 2011. Taking 60 seats or more in Quebec would make it much easier for the NDP to form the government in Ottawa.

There was a lot riding on the French-language debate. Mulcair had the opportunity to halt these negative trend lines and perhaps reverse them. Conservative Leader Stephen Harper was looking to secure some gains in Quebec in order to make up for losses elsewhere. Liberal Leader Justin Trudeau is in dire need of a large number of seats in Quebec if he is to win, and Gilles Duceppe is fighting for the very survival of his party.

No pressure.

CBC's Poll Tracker aggregates all publicly released polls, weighing them by sample size, date and the polling firm's accuracy record. Upper and lower ranges are based on how polls have performed in other recent elections. The seat projection model makes individual projections for all ridings in the country, based on regional shifts in support since the 2011 election and taking into account other factors such as incumbency. The projections are subject to the margins of error of the opinion polls included in the model, as well as the unpredictable nature of politics at the riding level. The polls included in the model vary in size, date and method, and have not been individually verified by the CBC. You can read the full methodology here.