You know the stakes are high in a general election campaign when the mother of one of its leaders steps in to defend her offspring. “I think it’s straight-out bullying,” Margaret Trudeau told CBC Radio in April, referring to the series of negative ads aimed at her son Justin, the leader of the Liberal Party of Canada.

From picking holes in his foreign policy and showing him performing a striptease to highlighting the “merits” of his hairstyle, the Conservative-backed attacks on Justin Trudeau have been a “relentless” part of the general-election campaign, says John Doyle, a columnist at The Globe and Mail newspaper.

“In Canada people have been dismayed by the arrival of attack ads over the past decade or so,” he says. “The thing is though, they’re effective. They’re very simple-minded but then simple-minded tends to work in television advertising, especially in politics.”

In one of the tightest election races in recent memory, the attack ad has become a potent feature and a key part of Conservative re-election strategy. “I don’t think Canadians realise how comparatively nasty our politics are,” says Peter Loewen, assistant professor at the University of Toronto’s School of Political Science. “Even from a century ago, the election literature is incredibly nasty and personal.”

Those twin features of political advertising may have found a comfortable home in the 2015 general election campaign but they are nothing new according to Erin Tolley of the University of Toronto: a 1993 advert by the Conservatives appeared to mock the facial paralysis of then Liberal leader Jean Chretien.

The current prime minister, Conservative Stephen Harper, has been in office for nearly a decade but knows he has a stiff fight ahead if he is to secure a third term. “Most politicians want to be liked,” says Jonathan Malloy of Carleton University in Ottawa. “But this is a government that only listens to its base. Harper really doesn’t care if the broad church of the country likes him.” Reframing the debate away from policy by highlighting his opponents’ perceived weaknesses may be his strongest card.

“Attack ads work when they help crystalise a pre-existing set of doubts about a candidate,” says Jonathan Kay, editor in chief of The Walrus magazine. Harper’s main opponents – the New Democratic Party (NDP) and the Liberals – have largely steered clear of negative strategies. “They have suggested they want to engage in more positive politics,” says Tolley.

But it may be a challenge for voters to pick out any positives in this election: Canada’s economy has contracted month on month for much of the year, the Canadian dollar has slumped and political scandals have chipped away at public confidence. Personality politics may, therefore, step into the vacuum created by the resultant disillusionment.

“Voters complain that these ads are an awful thing,” says Paul Wells of current-affairs weekly Macleans. “But since parties that run them often win elections, they’re willing to put up with complaints.” Even if the complaints come from the mothers of those under attack.

Three low blows that hit home:

1988: ‘Free Trade Deal’ (Liberal)
Featuring the US-Canadian border being scrubbed out, this ad framed much of the Free Trade debate that became the central issue of the 1988 general election campaign.

2005: ‘Christmas Gift’ (NDP)
A jaunty ad that implied giving Stephen Harper “the boot” for Christmas, starring NDP leader Jack Layton, who died suddenly in 2011.

2009: ‘Just Visiting’ (Conservative)
The political ambitions of Liberal leader Michael Ignatieff were dismantled by ads that portrayed him as a globetrotting cosmopolitan, “just visiting” Canada and with little understanding of the issues facing the country.

Venezuela’s petrodollars no longer cover its debts, Brazil’s ultra-deep-water bids foundered on onerous contract terms and Argentina’s byzantine fiscal policy makes above-ground shale exploitation more challenging than drilling. In a region where oil is an abundant but often mismanaged resource, Mexico’s disappointing inaugural oil auction in July – beset by falling crude prices and hobbled by a state promise to heavily tax profits – seemed a chronicle foretold.

But the government has responded with sweetened terms and a revised timetable for those prized deep-water bids next year. The country could yet prove the exception to the rule.