Less than a year ago, the Liberals under Justin Trudeau were comfortably leading in the polls, their victory against a tired Conservative government and drifting NDP opposition looking all but inevitable.

Today, the party is losing steam and in danger of dropping out of a three-way race with its erstwhile floundering opponents.

That the Liberals have been slumping in the polls for months has been overshadowed by the sudden NDP surge since the victory of its provincial cousins in Alberta in May. But the Liberal slide has been prolonged and significant.

The Conservatives currently lead in ThreeHundredEight.com's polling averages with 31 per cent support, with the Liberals at 29 per cent and the NDP at 28 per cent. But that represents a dramatic shift in a short period of time.

As recently as October, the Liberals were averaging 36 per cent support in the polls, putting them seven points up on the Conservatives and 12 points ahead of the NDP. Since then, the Liberals have dropped seven points, with four of those points going to the NDP and two to the Conservatives.

Worse, the Liberals' decrease has accelerated. The party was polling at around 34 or 35 per cent between November and February, and still enjoyed a lead over the Conservatives. But by the beginning of March, they were down to 33 per cent, and by the end of that month, 31 per cent. The Liberals have lost about four points over the last three months, compared to a three-point drop in the previous five.

The Liberals led in virtually every single poll from the day that Justin Trudeau became leader in April, 2013 to the end of last year. But over the last 16 national surveys, the Liberals have led or been tied for the lead in only four.

The drop in support for the party has coincided with softening numbers for Trudeau as well.

In Nanos Research's weekly rolling polls between November and April, Trudeau was generally the choice of 30 to 31 per cent of Canadians as the best prime minister, against 30 to 34 per cent for Stephen Harper and 17 to 19 per cent for Thomas Mulcair. But in the survey published this week, Trudeau stood at just 27 per cent, behind Harper (29 per cent) and just ahead of Mulcair (25 per cent).

NDP eating into Liberal support from coast to coast

No one part of the country has been responsible for the slide in Liberal support.

In British Columbia, the Liberals stood at 34 per cent in mid-February, but have since dropped seven points. The New Democrats have gone from just 22 per cent to 31 per cent over that time, while the Conservatives have held steady.

The Conservatives have also been holding their own in the Prairies and in Atlantic Canada, whereas the Liberals have slipped. In Saskatchewan and Manitoba, the Liberals have gone from 31 per cent just a month ago to 27 per cent today. The NDP, meanwhile, has jumped from 20 to 25 per cent. The New Democrats are up eight points in Atlantic Canada since early March, while the Liberals have decreased from 52 per cent to 45 per cent.

In Ontario, the Liberals were polling as high as 42 per cent in October. They were still at a relatively robust 36 per cent in mid-April, but have since fallen to 32 per cent. The Conservatives have taken a small step back here, from 36 to 34 per cent over the last two months, while the NDP has jumped six points to 26 per cent.

The downward trend for the Liberals in Quebec has been more gradual. The party was at 32 per cent from November to January before slipping to between 28 and 30 per cent through to March. They have since fallen more sharply to 25 per cent, while the NDP has picked up six points over the last month to lead with 34 per cent. The Conservatives have taken a hit here, dropping from 21 per cent to about 18 per cent, putting an end to the gains they had made in the province since the beginning of the year.

The Bloc, at 17 per cent, was hardly a factor in the race prior to this week. How Gilles Duceppe's return to lead the party will shift things remains to be seen.

Finally, the Liberals have also taken a big hit in Alberta, down eight points since just before the provincial election to 18 per cent. The NDP has picked up six points over that time, moving into second at 27 per cent. The Conservatives have also seen their support increase as memories of the provincial vote fade. They have gone from 44 to 49 per cent.

This all adds up to a worrying picture for the Liberals.

After leading in the polls for so long, momentum is turning against them at the worst possible time. They will have the opportunity to reverse these trends once the election campaign begins in earnest. But rather than campaigning as the front runners, the Liberals could find themselves chasing the Conservatives and New Democrats once the writ finally drops.

ThreeHundredEight.com's vote and seat projection model 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.

Éric Grenier's regular column on polls and polling trends will return June 30.