Finding the right political balance between the environment and the economy isn't easy for any party. For Justin Trudeau's Liberal government, it's especially awkward.

The dispute over the expansion of the Trans Mountain pipeline is only the most recent — and potentially the most volatile — example of this problem.

British Columbia's government doesn't want the project to go ahead. Both the federal government and Alberta Premier Rachel Notley argue that the pipeline expansion is in the national interest and say B.C. Premier John Horgan should back down.

Adding to the urgency is the deadline imposed by Kinder Morgan, the company behind the project. It wants government assurances by the end of next month that the pipeline can be built.

On Sunday, Prime Minister Trudeau will sit down with Horgan and Notley in Ottawa for a meeting that will require an unscheduled pit stop between the prime minister's trips to Lima, Peru and Paris, France.

Federal NDP Leader Jagmeet Singh, also trying to mediate between two NDP premiers, wants the federal government to join B.C. in a Supreme Court reference to decide on jurisdictional issues. The federal Conservatives have long called for Trudeau to do more to get B.C. to drop its actions against the pipeline.

The Liberals say that all options are on the table, but insist that the pipeline will get built.

If they're right — if the Trans Mountain expansion is built — the Liberals can expect to pay a political price for it in British Columbia, where the project is deeply controversial. But would they stand to lose more support in B.C. if the pipeline goes ahead than they might in the rest of the country if it doesn't?

Lots to lose in B.C.'s Lower Mainland

On the face of it, the electoral calculation looks simple. In the 2015 federal election, the Liberals won four seats in Alberta, where the pipeline is very popular. But they won 17 in B.C. (and added an 18th in a byelection late last year).

Opinions on the pipeline are divided in B.C. A recent survey by the Angus Reid Institute found that British Columbians are split down the middle on whether the provincial government is right to delay the Trans Mountain expansion.

On the pipeline itself, 23 per cent of British Columbians said they strongly support it, while another 24 per cent say they strongly oppose it.

Opposition to the Trans Mountain pipeline project is greater in the Lower Mainland than in the B.C. Interior. (Dillon Hodgin/CBC)

But opinions are not uniform throughout the province. A poll by Insights West conducted last fall found that British Columbians in the Lower Mainland were twice as likely to strongly oppose the pipeline than they were to strongly support it. In the B.C. Interior, where resource industries are major employers, more respondents strongly supported the pipeline than strongly opposed it.

Only one of the Liberals' 18 seats in B.C. is located in the Interior. The other 17 are in the Fraser Valley and the Lower Mainland.

So the Liberals have a lot more to lose in the Lower Mainland than in the rest of British Columbia and in all of Alberta — where the four seats the party won in 2015 likely amount to the best the party can reasonably expect there in the current political climate.

But this it isn't a simple matter of comparing the Liberals' meagre electoral prospects in Alberta to their more significant ones in British Columbia.

More to lose outside of B.C.?

Though the pipeline is a top-of-mind concern for British Columbians and Albertans, failing to get the project completed could have consequences for Liberals nationwide.

A poll commissioned by the Ecofiscal Commission and conducted by Abacus Data recently found that 60 per cent of Canadians agreed that "Canada should continue to develop its oil and gas resources and get them to markets while we are using carbon pricing and other measures to transition to a lower carbon future." Another 40 per cent of those polled agreed that the country needs "to take measures to greatly slow or stop development and transmission of oil and gas."

That 40 per cent is a significant minority, but it's already being fought over by the NDP, the Greens and (in Quebec) the Bloc Québécois. The Liberals' entire strategy of balancing the economy with the environment is aimed at the other 60 per cent.

Support for the Trans Mountain pipeline is strong in Alberta and Saskatchewan. (Mark Matulis/CBC)

This suggests that failure to get the Trans Mountain project completed could disappoint those Canadians who feel that the development and export of oil and gas is an important part of the country's economy. It could leave the Liberals looking like bad economic stewards and convince more voters that economic growth and a cleaner environment aren't two sides of the same policy coin.

In other words, the wheels come off Trudeau's plan to put a price on carbon if he doesn't also have a new pipeline to offer. And with provincial politicians like Jason Kenney in Alberta and Doug Ford in Ontario poised to become big players on the national stage, the prime minister doesn't need to give them any more ammunition in their fight against carbon pricing.

Not everyone likes a compromise

The hastily organized meeting between Trudeau, Notley and Horgan, and the last-minute change in Trudeau's travel plans, suggest the government has concluded it has more to lose nationally than to gain locally by letting Kinder Morgan throw in the towel.

Notley and Horgan have no such calculations to make — particularly Horgan, given that almost all of his party's seats are on Vancouver Island and in the Lower Mainland.

Singh, meanwhile, knows that his party's support is lowest in Alberta, highest in British Columbia. The NDP holds 14 seats in B.C., but just one in Alberta.

In Quebec, where the pipeline is least popular, the New Democrats can't afford to alienate any more voters. By backing B.C.'s request to put the dispute before the courts, Singh has apparently picked his side — and it isn't with Premier Notley, who once called Singh "irrelevant."

NDP Leader Jagmeet Singh has asked the federal government to join the B.C. government in settling jurisdictional disputes related to the pipeline at the Supreme Court. (Patrick Doyle/Canadian press)

The Conservatives' supporters are almost uniformly in favour of the pipeline. They have no need for any compromise at all.

If the Liberals manage it, balancing the economy and the environment is the kind of grand political compromise that can pay off in spades. The Abacus Data survey found that 84 per cent of Canadians say transitioning to a low carbon economy is a good goal, but 75 per cent say that the transition should be managed "in ways that are careful to not drive up the cost of living too much or cost too many jobs."

The alternative would be to repel both those voters who want to see the balancing act succeed and opponents of the pipeline who will not forget that Trudeau supported it.

What's at stake here for the Liberals is not the fate of a few seats in the Lower Mainland, or the party's tenuous hold on its beachheads in Alberta. It's the argument that the prime minister has made, time after time, that — between the NDP and the Conservatives — the Liberals' middle road is the path forward.