Like most recent polls, one released this week by Abacus Data suggests an unpredictable three-way race in which the Conservatives, New Democrats and Liberals are all within a few percentage points of each other.

But beyond the horse-race number was a far more intriguing finding that challenges one of the most common assumptions about the coming federal election's dynamics – and would be highly unsettling for Stephen Harper if true.

If there is one thing we're supposed to know about the modern Canadian electorate, it's that the Conservative base is rock solid. Somewhere in the range of 30 per cent of us, according to this bit of received wisdom, only have eyes for the governing party – which is a much higher floor than either of the other leading parties enjoys, seems to preclude the possibility of a complete Conservative collapse, and requires Mr. Harper to win over only a relatively small number of swing voters in order to win elections.

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When Abacus tested the firmness of each party's support, with an online panel of 1,500 voting-age Canadians surveyed between May 28 and 31, it found something very different.

While the Conservatives did appear to have more locked-in supporters than the other two parties, a majority of the 31 per cent of people who said they would vote Conservative if an election were held tomorrow still seemed willing to consider other options before the real election day.

Among all respondents, only 9 per cent both identified as Conservative supporters and agreed with the statement "I know how I will vote and it won't change." That was better than the same responses for the Liberals and NDP, which each got 6 per cent, but not dramatically so.

In a separate set of questions seeking similar information, 15 per cent of respondents said they would only consider voting for the Conservatives. That was higher than the 10 per cent who said they would only consider voting Liberal, but not the 16 per cent who said they would only consider voting NDP.

Here, some healthy skepticism is in order, and not just because it's only one poll (though that's a good reason in itself). Survey respondents may think it sounds better to say they're open-minded about their choices – and may like to think they are – even if there's little chance of them actually moving. There is absolutely no historical precedent to suggest the minimum share of supporters for the lone conservative option in a national election could fall off a cliff. And the Conservatives have very strong data on their past supporters – who has voted for them, who has given money and so on – which should make a big difference in getting those people to cast ballots for them again.

But with the Conservatives' faith in their ability to mobilize past supporters and others' near reverence for their ability to do so, there is some danger in mistaking roughly a third of the electorate for robots.

If you watched Alberta's Progressive Conservatives suddenly go from dynasty to third place, or the Bloc Québécois get virtually wiped out of their province in favour of a party that previously held only one seat there, or even Ontario's provincial Tories accidentally turn off people they were sure would support them, it is not all that shocking a proposition that some members of the federal Conservatives' fabled base might at least consider going elsewhere.

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It is enormously unlikely that enough of them will make good on such thoughts to plunge Mr. Harper's party anywhere near as low as 15 per cent popular support, let alone 9 per cent. But because relative to the other parties the Conservatives make little effort to win over new supporters – focusing primarily on mobilizing their 30-odd per cent and trying to persuade just enough additional voters to put them over the top for a majority government – even a limited erosion of their base could spell electoral disaster for them.

In some elections, such as Alberta's, even seemingly reliable supporters of the status quo decide they've had enough of it. In others, like Ontario's, they unexpectedly rally around incumbents because the alternatives are deemed unpalatable. So for all we know, even voters the Conservatives aren't counting on at the moment could wind up casting ballots for them.

The Abacus poll is, more than anything else, a reminder that even some of the most supposedly predictable voters are capable of surprises once a campaign begins in earnest.