Slinging mud at political opponents is a long-standing tradition in democracies around the world.

In the days before broadcasting and the internet, public speeches, newspaper articles and editorial cartoons were the catapults of choice to fling accusations of corruption or incompetence. It helped that many publications were flagrantly partisan, and not just on their editorial pages. Publishers, editors and writers would co-operate with political parties on the best way to attack the other side — something that was widely known and accepted.

In Canada, one famous cartoon in an anti-Conservative party magazine showed the prime minister of the day, Sir John A. Macdonald, telling his Liberal opponent that there was nothing wrong with bribing voters with money from business interests seeking government contracts. Macdonald lost the subsequent election, in 1874.

According to a 1998 study on negative campaigning in the United States, rising standards of objectivity and balance in journalism eased overt partisanship from news pages to advertisements in the first half of the twentieth century. Strict requirements for "fairness" in radio — and later television — news broadcasts had the same effect, the study says.

Born in the U.S.A.

Paid political advertising, as we know it today, was probably born with the U.S. Communications Act of 1934. It allowed broadcasters to refuse commercials for products or services, but required that political ads be aired as submitted by campaigns.

Overtly negative advertising appeared in Canada during the federal election of 1935, when the Conservative Party bought airtime for carefully scripted "chats" between actors playing ordinary people discussing corruption, intimidation and lying by the Liberal government of the day.

In the decades that followed, political campaigns became more focused and professionally run. Public relations and advertising agencies were increasingly influential. A certain conventional wisdom evolved. A campaign began with positive ads that put forward a candidate's strong points and only became negative in the closing days if that candidate was lagging behind in the opinion polls.

The 1964 U.S. presidential race, between incumbent Democrat Lyndon B. Johnson and Barry Goldwater of the Republicans, set an early, much-emulated benchmark for the "gotcha" negative political ad that was deliberately designed to provoke outrage but have a lasting impact.

Love each other, or die

The commercial began idyllically, with a little girl plucking petals from a daisy. A voiceover then kicked in with a male announcer counting down from ten with the camera jumping closer to the child's face with each number. At zero, a nuclear explosion, represented by a mushroom cloud, fills the screen. The voice of then-president Johnson is heard — referring only obliquely to his fiercely anti-Soviet opponent, then-senator Goldwater, "These are the stakes — to make a world in which all of God's children can live, or to go into the dark. We must either love each other. Or we must die."

The ad ran only once on NBC but sparked a furore. All three U.S. television network news programs covered the controversy. Letters to the editor and calls to TV station switchboards continued for weeks. Barry Goldwater asked for equal time to explain his position on the use of nuclear weapons against America's enemies. He got it, but that only kept the story running.

Bill Moyers, the then-presidential press secretary, confirmed the strategy in a memo to Johnson. "While we paid for the ad only once on NBC last Monday night," he said, "ABC and CBS both ran it on their news shows Friday. So we got it on all three networks for the price of one. This particular ad was designed to run only one time."

Such continuing coverage of the negative ads is, as Moyers pointed out, a decidedly beneficial side-effect that remains hugely relevant today. It's what advertising agencies call "free media" — news reports on the controversy surrounding a particular attack mean repetition of the ad's content, and growing voter doubt or cynicism over the issues involved.

Good cop, bad cop

While political scientists mostly agree that the electorate doesn't like nasty attack ads, they also concur that campaign strategists find them irresistible for many reasons. Not least of these is that ads run by political parties and advocacy groups like Canada's National Citizens Coalition, or MoveOn.org in the United States allow candidates to present themselves as above the fray, no matter how much has been slung in their name in the media.

"It's good cop, bad cop," says Evan Tracey of TNSMI Campaign Media Analysis Group, a company that tracks political advertising. He says this strategy allows parties to throw the sharp elbows and give the candidates plausible deniability.

This all helps to explain why today's political parties are wedded to negative advertising. During the U.S. midterm elections last year, campaigns spent 10 times more money attacking each other than extolling the virtues of their own candidates, a trend deplored by political scientists on both sides of the border.

"They [negative ads] don't always work," says University of Toronto political science professor Neil Nevitte, "In fact, in certain cases they can have the opposite effect — a too-personal attack can actually induce sympathy for a candidate."

A polite people, or not

In fact, it may be that Canada is growing less tolerant of negative campaigning than its neighbour to the south. "We're a more polite people," says Michael Adams of the Environics research and polling company in Toronto, "or at least we think we are."

Which begs the question about whether Prime Minister Stephen Harper's Conservative government will gain or lose from the ads attacking Liberal leader Stéphane Dion. Pollster Allan Gregg concedes that they just might.

The new ad campaign, he says, "feeds into both the general cynicism and the belief that no political party has got a particularly good agenda on the environment. It's probably smart politics. I don't know if it's good public policy."

Adams of Environics isn't so sure. "If he [Dion] has a plan, then attack it in Parliament. They [the government] are behaving like a political party just before an election. I'm not sure that works for them."