Stephen Harper will enter 2015 fighting his political opponents, of course, but more important, he will be fighting history.

Since Louis St. Laurent took office in late 1948, prime ministers with majority governments have never lasted more than 11 years in office before defeat or resignation. Their average time in office: seven years.

If Mr. Harper sticks to his own election timing law, Canadians will vote in October, 2015, by which time the prime minister will have been in office for nine years, eight months.

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Think of the prime ministers with majorities since 1968. Pierre Trudeau served 11 years (1968 to 1979) before being defeated. Brian Mulroney served a bit less than nine years before resigning. Jean Chrétien was prime minister for 10 years and a month before resigning.

By next fall, Mr. Harper will be around the cusp of when recent history suggests prime ministers leave office, either because the electorate boots them from office (Mr. Trudeau), because they sense they cannot win again (Mr. Mulroney), or because they cannot hold the party together (Mr. Chrétien).

Mr. Harper obviously senses he can win again, and he faces no internal party threat. What would remove him from office, therefore, would not be his sense of looming defeat or internal party strife – no, he would have to be defeated in an election. If history is any guide, defeat becomes more likely the longer a prime minister tempts fate, which this one is doing by asking for another mandate after almost a decade in office.

The most powerful anti-government sentiment in any democracy is the oldest adage in politics: "Time for a change." The economy can be reasonably sound, the political alternative untried, even shaky, the government experienced and able, but when the largest parts of the public settle on the ill-defined but powerful notion that the time has come to change, there isn't much the incumbents can do.

The tide comes in and those incumbents go out. It might be cruel and unjust, but it's also democracy's greatest safeguard against the arrogance of power.

Other democracies codify time in office: two four-year terms (the United States), one six-year term (Mexico), two five-year terms (France, Poland). British parliamentary systems let a prime minister carry on as long as he or she commands the confidence of the Commons, with elections every four or five years.

Without term limits, recent Canadian history suggests a kind of limit by convention. After a decade or so, the electorate arises, puts its hands in a "T" formation and says "Time's up."

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In Mr. Harper's case, about 60 per cent of the electorate made the "T" sign long ago, but he can win another majority under our first-past-the-post system with about 40 per cent of the vote. He did it in 2011. He obviously feels he can do it again, or quite likely he wouldn't try.

He has an unshakable core vote of 30 to 32 per cent of the electorate. These people skew older, rural, male, western Canadian – and they vote. The Conservatives know how to mobilize them.

They have also identified minority groups – Jews, Tamils, Ukrainians – and tied Canadian foreign policy to the interests of these slices of the electorate. They have large amounts of government money in the form of tax cuts and government advertising to direct at other slices of the electorate: single-income families with stay-at-home mothers, parents with kids in athletic programs. And they have a large series of targeted spending announcements yet to be made, on top of the dozens and dozens already made.

In this, Canadians see an immense contradiction in the Harper government. The government cuts all kinds of government services, slices taxes (which costs the treasury), preaches the virtues of a smaller state and expresses determination to balance the budget – all while sending Mr. Harper and his ministers across the country announcing new spending programs and projects.

With all these advantages, and with many more attack ads yet to be unleashed against the Liberals and their leader, Justin Trudeau, can the Conservatives win again? They only need 40 per cent, remember, and beyond Quebec, the opposition is divided three ways: Liberals, New Democrats and Greens.

Quite likely, the Conservatives fear their opponents less than the rhythms of history.