Readers are right to complain that political journalists focus too much on polls, obsessing on the electoral horse race rather than on the substance of the party platforms.

But sometimes you do need to pay attention to the horse race, and this is one of those times. Why? Because if the NDP can sustain its recent gains in francophone Quebec, Justin Trudeau's Liberals cannot win the next election. It's as simple as that.

A CROP poll in late May showed the NDP with 42 per cent of the votes in Quebec, streets ahead of the Liberals, who were at 25 per cent. A June 1 Ipsos poll mirrored the CROP numbers for the NDP and the Liberals. Other polls, including one released Friday by EKOS, also show the NDP strong and the Liberals weak, in Quebec.

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"We definitely feel the NDP is in very strong shape there," EKOS pollster Frank Graves wrote.

Youri Rivest, vice president at CROP, says the NDP strength in Quebec reflects what he calls "a fundamental change" in the province's politics, from the sovereigntist-federalist battles of the past to a struggle between the left and the right, with the NDP solidly in control of the left.

Mr. Trudeau was initially viewed by Quebec voters as "a fresh face," says Mr. Rivest. But the freshness has faded, and in any case, the last time Quebeckers gave the Liberals a majority of Quebec seats was in 1980, almost two generations ago.

"I think it will be very difficult," for the Liberals to turn things around, Mr. Rivest predicts. "I just don't see how."

And yet they must turn things around. For without a solid contingent of francophone Quebec seats, the Liberals cannot win the election and probably can't form the official opposition.

How can that be? Well, let's play a game.

Let's imagine that on Oct. 19, the New Democrats hang on to most of their 54 Quebec seats, but otherwise the Liberals have a stellar, break-out-the-champagne night.

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They win every one of the 36 seats they currently hold. And they take every seat currently held by the Conservatives in Atlantic Canada, a gain of 13. That brings them to 49.

They take 10 seats from the NDP in Quebec, gaining in Montreal and the Outaouais. That puts the Liberals at 59 seats as they cross the Ottawa River.

In Ontario, Mr. Trudeau has an impressive night. The Liberals defeat every Conservative in Toronto and split the rest of the GTA 50-50 with the Tories, who currently hold almost every seat. That gives the Grits an additional 20 seats. But they have wins elsewhere in Ontario, too: London, Kitchener-Waterloo, Ottawa. Let's add six more to the total. The Liberals leave Ontario with 85 seats.

They have a good night in the Conservatives' Prairie bastion, with gains in Winnipeg, Calgary and Edmonton. Let's say six more seats. That brings them up to 91.

And in British Columbia, they pick up another half-dozen seats in the Lower Mainland and on Vancouver Island, even though most fights in that region are Conservative-versus-NDP contests.

Congratulations, Liberals! You have 97 of 308 seats! You're probably in third place, again.

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But the House is expanding, from 308 to 338, with an additional 15 seats in Ontario, six each in Alberta and British Columbia and three in Quebec. Let's give the Liberals half the seats in Ontario and B.C., and one of the three seats in Quebec (the Conservatives are expected to take all six Alberta seats).

That brings the Liberal total to 109 of 338 seats. That might be enough for opposition-party status, if the NDP vote collapses outside Quebec. But if the New Democrats hold on to or expand their support in English Canada, the Liberals will be back in third.

As Ipsos pollster Darrell Bricker puts it: "If the Liberals can't form a geographic base somewhere in the country, especially Quebec, they can't win." An Ontario sweep, a la Jean Chrétien, isn't in the cards because the right is united and the left divided, unlike the 1990s when the opposite was true.

The situation for Mr. Trudeau isn't fatal. He and his team have done a stellar job of reviving moribund riding associations, recruiting volunteers and improving fundraising. The Liberal machine hasn't been this robust in many a year.

As Rivest points out, if Gilles Duceppe – who has returned to lead the Bloc Quebecois – can return the political landscape in Quebec back to a fight between sovereigntists and federalists, then Liberal fortunes could revive.

But the fact remains that Justin Trudeau has only four months to reverse a decline that has been underway now since last October. Above all, he must, he simply must, convince francophone voters in Quebec to rethink their commitment to Mr. Mulcair and the NDP.

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Otherwise it will not end well for him on election night, no matter what happens in the rest of the land.