As MPs prepare to make their way back to Ottawa for the return of Parliament, heralding the start of the new political season, the polls suggest that Justin Trudeau's Liberals are beginning to lose steam in national voting intentions.

A weighted average of the latest federal polls conducted to the end of September shows the Liberals have slipped two points over the past month, dropping to 34 per cent support. Both Stephen Harper's Conservatives and Thomas Mulcair's New Democrats have picked up a point, increasing to 31 and 24 per cent, respectively. The Bloc Québécois is up one point to 6 per cent, while the Greens have decreased by one point to 4 per cent support.

The relatively marginal shifts in support disguise a more significant change in the polls. After putting together an unbroken string of 20 federal polls in which the Liberals held a national lead – going back to even before Mr. Trudeau became Liberal Leader – the party has led in only two of the past four. These polls disagree with one another to an important degree, however, with the two polls putting the Liberals behind the Conservatives placing the margin at a single point, while the two polls giving the Liberals the lead gave them an edge of four or five points. The disparity is primarily in assessing where the NDP stands: in polls where the NDP is doing well, the Liberals have trailed the Tories, whose support is more consistent.

Story continues below advertisement

This three-point edge in the aggregate does not translate into a plurality of seats for the Liberals, who would likely win around 110 seats with these levels of support. That puts them 13 seats behind the Conservatives, who would win 123, while the New Democrats would take about 59 seats. The Bloc Québécois would regain official party status with 14 seats and the Greens would win two. Compared with the number of seats the parties were in a position to win a month ago, this represents a drop of five seats for the Liberals and 12 for the NDP, whereas the Conservatives and Bloc have picked up eight and nine respectively.

On the new 338-seat electoral map, the Conservatives would likely win 134 seats to 124 for the Liberals, 62 for the NDP and 16 for the Bloc.

Quebec remains the most dynamic political race in the country, with the controversies related to the Charter of Quebec Values spilling over onto the federal scene. The Liberals continue to lead on average, down three points to 34 per cent. The New Democrats trail with 26 per cent, while the Bloc Québécois has picked up three points to reach 23 per cent. The Conservatives bring up the rear with 13 per cent support.

But individual polls tell a more complex story. The Liberals had trailed in only one of 23 polls conducted before September going back to Mr. Trudeau's leadership victory, but have split the lead with the NDP in the last six surveys. As is the case nationally, however, the polls in which the Liberals lead award the party a comfortable margin: between seven and 13 points, compared to an NDP lead of one or two points. It is possible that the charter has boosted the Bloc to some degree as, though the average puts them exactly where they were on election night in 2011, they hit 30 per cent in a poll for the first time since November, 2011.

British Columbia might also be shifting, as the Conservatives have picked up seven points to move ahead with 34 per cent against 29 per cent for the Liberals (down two) and 28 per cent for the New Democrats (down three). After polls showing a close three-way race in the province, the last four polls in B.C. have featured the best Conservative results since the spring. The Greens continue to get their best results in British Columbia, with 9 per cent support.

Voting intentions in Ontario are mostly steady, with the Liberals down one point to 38 per cent and the Conservatives up one point to 35 per cent. The New Democrats picked up two points to improve to 22 per cent support in the province.

Elsewhere, the Conservatives continue to enjoy a wide lead in Alberta and the Prairies (though the NDP is up in both regions), while the Liberals are well ahead in Atlantic Canada. Of interest here is that the Conservatives seem to have slipped back down after a brief uptick in the Atlantic region in July and August.

Story continues below advertisement

The Liberal slump nationwide could continue as attention returns to Parliament Hill. The Conservatives have an opportunity to kickstart the last half of their mandate with a new Speech from the Throne and Mr. Mulcair will be given the chance to shine in Question Period once again. But both parties still have to play catch-up – a far cry from where things stood just over two years ago.

ThreeHundredEight.com's vote projection model aggregates all publicly released polls, weighing them by sample size, date, and the polling firm's accuracy record. The seat projection model makes individual projections for all ridings in the country, based on the provincial and regional shifts in support since the 2011 election. 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.

Éric Grenier writes about politics and polls at ThreeHundredEight.com.