A federal election this fall? Don't rule it out. Top Liberal Party strategist Gerald Butts says his party is preparing for that scenario, among others. While most speculation has centred on the possibility of Prime Minister Stephen Harper moving up the election date from next fall to next spring, the Liberals believe it's even possible he could drop the writ a month from now.

Mr. Harper's office has denied any intent to go to the polls early, but nothing is set in stone. As he has shown in the past, this Prime Minister isn't one to be deterred by convention or by hurdles such as a fixed-date election law.

His Conservative government is long in the tooth. It's nearing a decade in office, which is what you might call the natural life cycle for modern Canadian governments. Waiting for another year, a span that will include the Mike Duffy trial, may just increase the fatigue factor and the sense that it's time for a change.

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Here are four possible scenarios:

By the book. Mr. Harper waits until next October. The thinking here is that he needs the time to make up ground on the leading Liberals. Also, he doesn't want to risk alienating voters by changing the set October date. The timing of the Duffy trial, slated to run from April to June, is troublesome, but it's better than being seen as forcing an early election to avoid it. The image of being morally bankrupt (see last week's Paul Calandra fiasco) is already hurting the government. It doesn't want to fuel that perception.

Early spring. Mr. Harper brings in a February budget that contains highly controversial measures, then triggers an election on it for the end of March. Many would see this as blatantly opportunistic, coming just ahead of the Duffy trial. But Mr. Harper would rely on the hope that the timing is an issue only for the campaign's first few days, as we've seen in the past. Not to be ignored in these calculations is the chance that the Duffy charges could be settled out of court, or that the trial's timing is pushed back. No doubt, the Prime Minister's men will be pulling all strings possible to bring about such outcomes.

Early December. If Justin Trudeau's popularity numbers start to slide, Mr. Harper may pounce right away. There is concern in Liberal circles and hope in Conservative precincts that the reason Mr. Trudeau is rushing an autobiography into print (it will be released in three weeks) is that there are embarrassments from his past that he wants to disclose on his own terms, instead of leaving the deed to the Harper attack machine. The Conservatives have a budget update to deliver, and if they're gaining ground, they may use it – with some big tax-cut promises – as a springboard for a snap election. It would be three-and-a-half years into a majority mandate. Jean Chrétien went to the polls twice on a similar time frame.

Pass the torch. The PM reads the tea leaves/billboards and concludes that it's time. He calls a Conservative leadership convention to be held in February. The option has much to recommend it. He goes out as one of the big winners in party history, having moved the conservative agenda appreciably forward in many policy areas. He avoids the distinct possibility of a humiliation at the hands of a Trudeau.

Looking at these choices, the cautious wagering would be on the first option, the set date. But Mr. Harper is an aggressive tactician, well capable of rolling the dice. He is behind in the polls and has to shake things up somehow. In other words, expect the unexpected.