Of all the policies Justin Trudeau might introduce in his first term, it could have the most profound impact on the country's future governance.

But first, the Prime Minister's preferred change to how we hold our elections – a move to preferential balloting, in which candidates would ultimately have to achieve the support of a majority rather than a plurality of voters – requires a big sales job to a public for which the matter is barely on the radar yet.

Only a couple of months after Mr. Trudeau won power, and nearly four years before the effect of any electoral reform would be felt, his window to make that case is already closing. Because his Liberals are at risk of their opponents effectively putting the kibosh on ranked ballots by defining the issue before they even attempt to define it themselves.

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There is a strong case Mr. Trudeau could be making for why we should switch from first-past-the-post to a system in which voters mark second and third choices on their ballots, with last-place candidates eliminated and their supporters' votes going to those alternative choices until a front-runner has more than 50 per cent.

He could argue that it would put an end to parties being able to focus only on the less than 40 per cent of the electorate needed to win a majority government, and in some cases openly writing off large swaths of the population. And that it would allow Canadians to vote their conscience and vote strategically, rather than worrying that supporting the party of their choice might be a waste. And that, unlike proportional representation – the other major reform option, in which parties would be allotted some or all seats based on their share of the popular vote – it would still allow every MP to serve as a local representative.

But Mr. Trudeau can't argue any of that, or at least believes he can't, in any sort of sustained way. Nor is he delegating other Liberals to do so, or making much effort to line up outside groups that might take up the cause. Because, while committing to replacing first-past-the-post with something by next election, he insists that he is open-minded about what that something is, and doesn't want to prejudice coming consultations with parliamentarians and then the general public.

The problem is that he has already tipped his hand, by acknowledging before this year's election that ranked ballots are what he leans toward. That understandably was not lost on his political rivals. So the New Democrats (who favour proportional representation), the Conservatives (who want no major change to the voting system at all) and those sympathetic to either of those parties are diligently mounting an effort to convince Canadians that, if the Liberals put forward the preferential model, it will be nothing but a cynical ploy aimed at keeping themselves in power.

Their argument, and their impetus, is that as a centrist party that can avoid being anathema to either side of the spectrum, the Liberals stand to disproportionately benefit most from counting second choices. That contention is supported by analyses that suggest the Liberals would have won a much larger majority if ranked ballots had been in place by this year's election. (Political scientist Paul Fairie, writing for The Globe and Mail, assessed that it would have netted the Liberals roughly an extra 20 seats. Analyst Eric Grenier, writing for the CBC, suggests they would have won 224 ridings rather than the 184 they actually claimed.)

Mr. Trudeau pushed back a bit against that perception in a Canadian Press interview this week, on the basis that it might have been a completely different campaign if it had not been waged under first-past-the-post. Privately, his advisers make that argument a bit more forcefully. And it's indeed fair to wonder, for instance, if the Conservatives would have willingly alienated as many people with their anti-niqab posturing if polarization came with more consequences.

Still, in the absence of any co-ordinated and compelling pitch for what ranked ballots would achieve, other than stacking the deck, the impression that that's the whole purpose could soon take hold. Whether the Liberals opt to put the reform to a referendum, as the Tories are demanding, suspicion could run strong enough that it's a non-starter.

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Perhaps the Liberals will yet prove able, by accident or design, to shape the consultation process in a way that helps make ranked ballots palatable. But if his self-imposed dilemma causes him to miss his window, Mr. Trudeau will have to choose between a different electoral reform and none at all.