It’s taken for granted in political circles that opposition parties aren’t elected so much as governments are defeated. Or, put another way, governments aren’t defeated by anyone so much as themselves.

But however much voters want to get rid of a government, they need to know there’s a viable alternative. And there we have the biggest question heading into an election expected to be called tomorrow.

Short of taking out billboards explicitly asking Canadians not to vote for them, Paul Martin’s Liberals have done everything imaginable to drive themselves from office. From their non-existent policy agenda and their mishandling of the sponsorship scandal to their recruitment of an unabashed nationalist to run their Quebec operations and the civil war within their party, they’ve looked almost masochistic in their willingness to embarrass themselves.

This past week, they even managed to align themselves with Dalton McGuinty’s health-care premium. Rather than simply refusing to comment on a provincial issue, the Martinites decided it was a prime opportunity to contrast Liberal values with Conservative ones. Now Ontarians who don’t want to wait until 2007 to vent their frustration have been handed an opportunity to do so on June 28.

And yet, however much the Liberals look like the quintessential self-defeating government, the polls tell us otherwise. True, pre-writ surveys can’t be taken entirely at face value, especially when the Liberals traditionally drop several points as elections draw closer. But it’s hard to overlook that the narrowest poll result to date still placed the Liberals’ nearest opponents eight points back. And in every other survey, the Conservatives have hovered around the mid-20s.

It has already been argued that we’ve been here before. Jean Chretien was anything but a shoo-in in 1993, Mike Harris’s provincial Tories started off well back of Lyn Mcleod’s Liberals in 1995, and so on. But they were able to come from behind largely because their opponents enjoyed an artificial glow at the start of the campaign that quickly faded once voters got a good look at them.

This time, there’s no glow. Voters know exactly what the Liberals are all about. So the real ballot question is not “do the Liberals deserve to be re-elected?” but “are the Conservatives credible as a replacement?”

Considering that the Liberals are still expected to at least win a minority, the answer right now is no. Stephen Harper’s challenge is to change it.

That doesn’t mean he needs to light any fires. But it does mean easing moderate voters’ concerns on several fronts.

First, there’s policy. But Mr. Harper’s problem is less with what he’s advocating — there’s nothing all that radical, and if the numbers don’t add up, that certainly didn’t stop the Ontario Liberals — than how he’s advocating it.

As pollster Frank Graves suggested this week, the Conservative leader has never been able to create a “sense of optimism.” While he’s not as gloomy as he used to be, he still seems so sour about the country’s prospects that he comes off as almost contemptuous. As corny as it may sound, he needs to learn — quickly — to frame his policies as a positive vision for the country, not a critique of what’s wrong with it.

Then there’s professionalism. The Liberals, having run the country for 10 and a half years (even if they’re loathe to mention the first 10), have built up enough credibility to get away with the odd flub. The Conservatives, most of whom have never been anywhere close to power, haven't. But while they’ve improved, there’s still a certain amateurism, fuelled partly by a hypersensitivity to criticism, that tends to cloud their operations and communications. And if that’s not enough, they also have to hope a slew of novice candidates — some of whom lack polish, to put it mildly — can be trusted not to pull a Betty Granger.

Finally, there’s Mr. Harper’s record. Liberal attempts to paint him as a religious nut will probably backfire, because they’re fundamentally dishonest. But attacks on actual positions he’s taken — from supporting the Iraq war to advising Albertans to take their lead from Quebec separatists — will resonate unless he does a better job of defending himself. Merely getting mad at the Liberals for having the audacity to attack him with his own words won’t reassure anyone.

That a moribund Liberal party is still positioned to win at least a minority government suggests that, as of now, most Canadians still don’t think Mr. Harper is ready for prime time. In five weeks, a referendum on his suitability to lead the country will tell us whether anything has changed.