It is clear Harper did not have to go for an election now. He was doing quite well in Parliament by playing the different opposition parties against each other. None of the opposition parties really seemed eager for an early election, so the Conservatives usually got their way without too much trouble.

Harper has not given a clear answer to why the election was necessary. Apparently he claimed in a speech it was because the Parliament was dysfunctional but in the latest leader's debate yesterday he denied saying that. His latest answer was that Parliament was about to reach an impasse.

I suspect the major driver for the election was that Harper saw an opening which might enable him to pick up more seats for either a larger minority or even a majority government. His party was doing better and the opposition parties less well, than at the 2006 election, in opinion polls before the election was called.

The most critical political responsibility of the Prime Minister, in a Westminster style system, is to choose the right election date for maximum party advantage. Do it right and you are revered as a great and successful leader (at least for a few weeks). Get it wrong and a despised failed leader is in severe danger of an abrupt end to his political career.

One possible point Harper may have been concerned about was, that if the election was delayed, then the Liberals might have changed to a new more credible leader.

Harper may also have thought that he could get the election out of the way before the world economic crisis had a major impact on Canada. If that was part of his thinking, the plan was overtaken by the pace of events.

Insofar as American events influenced the Canadian decision, Stephen Harper may have thought John McCain would do better and Obama worse than seems to be the case. I imagine Harper has most of his American contacts with the right wing part of the US population, so they may have indulged in mutual wishful thinking. To be fair also, Obama has only gotten far ahead of McCain since the writ was dropped (an idiosyncratic Canadian phrase, we do not use in the UK) for the election.

I suspect Harper would be attacked as the Canadian Bush whenever the election was held, so that may not in itself have been a major factor in a decision to go for an election now.