Though the Liberals and Progressive Conservatives have dominated the political history of New Brunswick, other parties have made their mark over the last two elections. They could do so again on Sept. 24, with potentially significant results.

With the exception of the 1991 election, when the Confederation of Regions party formed the official opposition, the 2014 election set a modern record for the proportion of New Brunswickers voting for a party other than the Liberals or PCs: 21.7 per cent, up from the 16.1 per cent combined vote share of the Greens, New Democrats and People's Alliance in 2010.

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The record could be broken again. The New Brunswick Poll Tracker, an aggregation of all publicly available polling data, suggests the three smaller parties could take a total of 22 per cent of the vote this Sept. 24.

Despite these gains, only the Liberals and PCs were able to win seats in 2010 and the Greens eked out just one seat in 2014.

Since 1974, a grand total of 14 seats have been won in general elections by parties other than the PCs and Liberals. Eight of those were CoR seats in 1991 and former NDP leader Elizabeth Weir was responsible for another four.

These are the topics New Brunswick voters care about the most in the upcoming election. 1:20

Accordingly, the charge is regularly levelled by partisans of the established parties that these minnows are splitting the vote with little to show for it.

It assumes, perhaps unfairly, that one of the established parties should be the natural home of supporters of the Greens, NDP or People's Alliance.

It is rarely as simple as that.

Nationwide, the Liberals and New Democrats share many voters. But Dominic Cardy, the New Brunswick NDP leader from 2011 to 2017, is now running as a PC candidate in Fredericton West-Hanwell, and one of the best-performing NDP candidates in 2014 was Bev Harrison, who sat as a PC MLA for nearly a quarter-century. Sometimes the political spectrum isn't a straight line.

Splits go every which way

Nevertheless, there were many ridings in 2014 in which the margin between the Liberal and PC candidates was smaller than the number of votes cast for either the Green, NDP, or People's Alliance candidate.

Enough voters supported the NDP in 21 ridings to theoretically change the outcome — the PCs won 13 of these races, suggesting the party might have been the main beneficiary of an NDP-Liberal "vote split."

There were 10 ridings in which the number of Green votes was greater than the margin of victory. The Liberals won six of those.

And in five ridings, the People's Alliance received enough votes to make the difference. The Liberals won four of those, enough to have put Brian Gallant in the premier's office.

People's Alliance Party Leader Kris Austin fell 26 votes short of the PCs in the riding of Fredericton-Grand Lake in 2014. (Catherine Allard/Radio-Canada)

Enough votes were cast for smaller parties in the 2014 election to theoretically change the government.

Had more of them voted for the PCs, David Alward's government could have been re-elected. But it would have required more than just the votes cast for the People's Alliance, the party that shares the biggest pool of voters with the PCs. Greens and New Democrats would have had to vote PC, too.

In 2010, however, Alward's margin of victory was large enough that support for the smaller parties was immaterial to the outcome. Shawn Graham's Liberals would have needed every vote cast for the Greens, NDP and People's Alliance that year in order to squeak out a one-seat majority.

And the split does not always benefit the same party. In 2006, support for the NDP was greater than the margin of victory in 13 ridings but it was the Liberals who won eight of these, and not the Tories who benefited from the split.

Who you calling a splitter?

The smaller parties, however, could also blame the Liberals and PCs for splitting the vote in a few ridings.

In the last election, Cardy and Harrison lost to the PCs by fewer votes than the number cast for the Liberals and Greens in their respective ridings. People's Alliance Leader Kris Austin only needed 27 of the 3,566 votes cast for the Liberal, Green and NDP candidates in his riding to beat the Tories' Pam Lynch.

And then there are splits within splits. In addition to Cardy's riding, the NDP could have won Saint John Harbour if the Greens had not "split" the vote.

In 2010, former NDP leader Roger Duguay lost to the PCs' Claude Landry in Tracadie-Sheila by 1,295 votes. The third-place Liberal candidate finished with 1,478 votes.

It is perhaps a difficult case to make to voters that a greater variety of opposition voices is needed in the legislature rather than an MLA with a plausible chance of being part of government. But that is the challenge that smaller parties face in every election across the country.

Potentially big impact in many ridings

That is the pitch that smaller parties are making in this campaign. New polling data from Corporate Research Associates in Halifax suggests that the Greens and People's Alliance might have the best chance of success.

In a survey conducted between July 19 and Aug. 8 in New Brunswick's three largest cities, the polling firm found that the Greens and People's Alliance had roughly doubled their support in Fredericton from the 2014 election. The poll suggested the Greens were up by about 12 points from roughly 10 per cent in 2014, and the People's Alliance was up five points from about six per cent.

That suggests that Green Leader David Coon is probably in a good position to secure re-election in his riding of Fredericton South. The gain for the People's Alliance might be enough to push Austin ahead in Fredericton-Grand Lake, especially considering the poll found no net gain for either the PCs or the Liberals in the city.

NDP Leader Jennifer McKenzie is running in the riding of Saint John Harbour, which the party held under former leader Elizabeth Weir in the 1990s and early 2000s. (Hadeel Ibrahim/CBC)

But the poll does not bode well for NDP Leader Jennifer McKenzie, running in Saint John Harbour.

The New Democrats captured about 20 per cent of the vote in Saint John in 2014 but the survey suggests their support has been cut in half in the city. Unless McKenzie is withstanding those trends while fellow New Democrats in other ridings bear the brunt of that drop in support, her odds of winning the party's first seat since 2003 could be poor.

However, even if the small parties combine for only one, two or even three seats in the legislature they will still have a wider impact.

The New Brunswick Poll Tracker's seat projection model finds the PCs ahead in seven seats in which their lead over the Liberals is estimated to be smaller than the share of the vote awarded to the Greens. There are six ridings in which the New Democrats are playing that "spoiler" role.

And for the Tories, there are six seats in which the People's Alliance is projected to have more support than the Liberals' estimated margin of victory over the PCs.

These are rough calculations based on where the polls are today and how these ridings have voted historically. But it is generally in line with the role that the smaller parties played in the 2014 election.

The polls suggest they could play that role again in 2018 — and if the race gets tighter as election day approaches, it could make a big difference.