Why attack ads might not be the zero-sum game party strategists are betting on.The gloves are off. The two leading parties are now running negative ads. Not contrast ads in which the attack on the opponent is followed by the attacker's contrasting position. Instead, both parties have gone nuclear with just over two weeks left. They are adopting what some are calling “American-style” attack ads. Are Canadian politicians now engaging in the same dirty politics that have become so toxic in America? It might be an outgrowth of this pandemic election without a reason, and the anger we've seen on the campaign trail. However, history shows that none of this is new, at least not for the Conservatives.Long before the recent Willy Wonka parody, the Conservatives ran negative ads aimed at framing newly elected Liberals leaders. Stéphane Dion was not a leader. Michael Ignatieff was just visiting. And Justin Trudeau was just not ready. This, combined with a barrage of highly partisan government advertising about Canada's Economic Plan helped keep the Conservatives in power for a decade and the Liberals in third position.Justin Trudeau ran on a positive message of change in 2015 and against the politics of division. There was no place for attack ads in the party's advertising strategy. The Liberals took a similar position in 2019 with Trudeau predicting the campaign would be the dirtiest and promising to take the high road. But that didn't prevent them from capitalizing on an old clip of Andrew Scheer explaining his opposition to same-sex marriage.While Trudeau still speaks about uniting rather than dividing Canadians, about optimism instead of fear, his ads now tell a different story. Even his former principal secretary, Gerald Butts, recently tweeted that “These are very strong ads by LPC. Tough and totally fair because they use O'Toole's own words and accurately depict Conservative policies to describe what's at stake in #elxn44”. Totally fair? You be the judge: “Take Back Canada”, “In His Own Words”, “The Record”. Add to this the 6 million dollars the party has spent so far on Facebook ads that often attack O'Toole and it's clear the Liberals are taking no prisoners this time.The Conservatives responded within hours with their own attack ads: “Negative Justin”, “Justin Says”, “What Do You Think?”.Zero-sum gameZero-sum is often misunderstood as meaning that nobody wins and nobody loses. It means the opposite: in a competitive situation, one side can't win unless the other loses. When the losses are subtracted from the gains, the sum is zero.This election likely won't be a zero-sum for either party. Each party's negative ads could essentially cancel the other party's attack ads. They'd be no winning, just degrees of losing and a whole lot of bruising.The limited impact of political advertising - positive and negativeThere is no conclusive evidence that attack ads are effective. Just like any ads, some are, some aren't. The political ad gurus who created hundreds of “American-style” ads for the Lincoln Project during the last presidential election argued that they all had their desired effect. That's highly questionable when no quantified evidence of each ads' cause and effect is provided. Despite all the science and expertise required to create political ads, their persuasion effect is surprisingly limited.A study released last year co-authored by political scientist Alexander Coppock, resident fellow at Yale's Institution for Social Policy Studies and the Center for the Study of American Politics, showed that, regardless of content, context, or audience, 'American-style” political ads do little to persuade voters.The study published in the journal Science Advances, measured the persuasive effects of ads from the 2016 presidential campaign among 34,000 people. It confirmed prior research suggesting that political ads have little impact on voters' intentions and that that those weak effects are consistent irrespective of a number of factors, including an ad's tone, timing, and its audience's partisanship.“There's an idea that a really good ad, or one delivered in just the right context to a targeted audience, can influence voters, but we found that political ads have consistently small persuasive effects across a range of characteristics,” said Coppock. “Positive ads work no better than attack ads. Republicans, Democrats, and independents respond to ads similarly. Ads aired in battleground states aren't substantially more effective than those broadcast in non-swing states.”The study does not demonstrate that political advertising is always ineffective: “The effects we demonstrated were small but detectable and could make the difference between winning and losing a close election.”Perhaps these ads will make the difference. Or we might witness the political equivalent of MAD - mutually assured destruction - leaving us all shaking our heads in disbelief.Éric Blais is the president of Headspace Marketing in Toronto. He has helped build brands for over 35 years and is a frequent commentator on political marketing, most recently on CBC's Power & Politics.