In 2007, Tom Mulcair — then in self-imposed exile from Quebec politics — pulled off an unlikely win in a federal byelection, taking the Liberal stronghold of Outremont for the NDP.

It was only the second time the NDP had won a seat in Quebec. But from this narrow beachhead, Mulcair and then leader Jack Layton dramatically grew their support in the province.

Their effort, of course, culminated in the Orange Wave, when the party won 59 of Quebec's 75 seats in the 2011 general election and stormed into Opposition.

Since then, though, NDP support in Quebec has slowly frittered away.

Under Mulcair's leadership, it was cut down to 16 seats in the 2015 election. Early predictions ahead of this fall's contest suggest the party won't win more than a handful of seats, if that.

It is fitting, then, that the Orange Wave's last stand seems to have begun with a byelection Monday in the riding where it all started: Outremont.

Mulcair's shadow

The seat became open when Mulcair quit federal politics last summer, after carrying much of the blame for the party's disappointing performance in 2015.

Julia Sanchez, a former international development executive who lived in Ottawa for many years before recently moving back to Outremont, is now carrying the NDP banner.

NDP Leader Jagmeet Singh campaigned with Julia Sanchez in December. He has been focused on winning his own byelection race in the Vancouver-area riding of Burnaby South. (Graham Hughes/Canadian Press)

She acknowledged the former leader's shadow still looms large in the riding. His name, she said, "comes up all the time. People were proud of Thomas Mulcair."

One name that doesn't come up much in the riding, or elsewhere in Quebec, is the NDP's current leader, Jagmeet Singh.

His profile is particularly low in the province, and he was last spotted in Outremont in December.

Singh has been spending most of his time on his own byelection race in Burnaby South, where a loss Monday could be fatal to his leadership.

Sanchez, meanwhile, has been counting on support from the remaining local NDP heavyweights.

Montreal MPs Hélène Laverdière and Marjolaine Boutin-Sweet — two Orange Wavers who won't run in the next election — have been stumping for her. So too has Charles Taylor, the 87-year-old philosopher who has run for the party several times.

"If we can get our people, our base, out to vote … then we will win," Sanchez said during a recent interview at a cafe in the riding.

Prime Minister Justin Trudeau campaigning with Rachel Bendayan in January. Bendayan first ran in Outremont in 2015. (Paul Chiasson/Canadian Press)

But the party's sympathizers are tempering their expectations ahead of Monday's vote.

"In this byelection the NDP is actually the underdog," said Karl Bélanger, a former NDP strategist who worked closely with Layton and Mulcair.

"If the NDP finishes with a strong second place, that would already be a win for the party."

The most likely scenario on Monday, in his view, is for Outremont to return to the Liberal fold. Before Mulcair's win in 2007, the Grits had held the riding almost continuously since the 1935 election.

The Liberal candidate, Rachel Bendayan, a lawyer and former party staffer, ran against Mulcair in the last election, finishing second by more than 10 points.

This time, she said, she benefits not only from a bit of name recognition, but also the record of the Trudeau government, pointing to investments in public transit, social housing and the Canada Child Benefit.

The Liberals, though, are heading into Monday's three byelections weighed down by the controversy surrounding the government's alleged interference in the prosecution of Quebec engineering giant SNC-Lavalin, which is accused of bribing Libyan officials.

Several recent polls suggest Liberal support has suffered in the wake of the scandal, and they are now in a dead heat nationally with the Conservatives.

Bendayan, though, doesn't believe the scandal is registering with voters in Outremont. "I haven't heard much about it at the doors," she said.

A test of progressive bona fides

Outremont, in many ways, is an atypical riding in Quebec, so the results of Monday's vote may offer little foresight of what will happen in October's federal election.

French-speakers make up less than 50 per cent of Outremont's population, according to 2011 census figures. There are large communities of immigrants in one part of the riding; affluent francophones and progressive-leaning students in another.

French-speakers make up less than 50 per cent of Outremont's population, according to 2011 census figures. There are large communities of immigrants in one part of the riding; affluent francophones and progressive-leaning students in another. (CBC)

Though the Conservatives, the Bloc Québécois, the Greens and Maxime Bernier's upstart People's Party of Canada are all running candidates, none of them is expected to be a factor.

It is, for all intents and purposes, a two-way race between the NDP and the Liberals.

With candidates for both parties indicating the environment is a major concern of voters, the Outremont byelection is providing a test of their progressive bona fides.

"People would like to see action on the environment, and they are very happy to have the leadership of the current Liberal government, particularly when we introduced the price on pollution," Bendayan said.

Sanchez, the NDP candidate, countered that the Liberals sacrificed their claim to climate leadership when the government bought the Trans Mountain pipeline.

"It really triggers disbelief, confusion and disillusionment," she said. "How is it possible we spent all this money to buy an old pipeline?"

But the import of these policy differences may be offset by the low voter turnout that tends to characterize byelections, especially those in the dead of winter.

"That's when the machines come into play," said Bélanger, the former NDP strategist, referring to the organizational resources parties can mobilize on election day.

If nothing else, Monday's vote will offer a glimpse of how much remains of the mighty NDP machine in Quebec.