Justin Trudeau was the golden boy of Canadian politics when elected prime minister, with doubts about his experience overtaken by a surprise and decisive victory for his Liberal Party in 2015 polls. 

Trudeau's progressive values seemed unimpeachable, and as leader he helped boost Canada's status on the global stage – aided from 2017 by comparisons with his neighbor to the south.

A pair of scandals – the SNC Lavalin affair and the blackface photo revelations – have punctured Trudeau's balloon, yet his Liberal Party's poll ratings are rising as the October 21 election nears.

A Canadian Broadcasting Corporation tracker aggregating public polling shows Trudeau's party has climbed ahead of the opposition Conservatives, led by Andrew Scheer, after months of trailing behind. Six months ago the Conservatives were six points clear, now the Liberals hold a narrow polling advantage that would translate into it becoming the biggest party in the House of Commons. 

On Monday evening, the race entered a critical two hours in the campaign's only official English-language debate. The neck-and-neck race is unusual in Canadian electoral politics, making the debate all the more important: A small change in the dial could make a big difference to the makeup of the next parliament.

Trudeau was an inevitable target: In a segment in which leaders could question any rival on stage, the prime minister was often the chosen one. The prime minister came under fire over his approach in office on climate change and on tax, the dominant theme of the debate and clear dividing lines between the Liberals and Conservatives. 

A particularly fiery exchange came between Scheer and Trudeau, with the Conservative hitting out over the SNC-Lavalin scandal and the Liberal leader responding by accusing Scheer of hiding the costings of his tax cut plan.   

"What we have here is Scheer and Trudeau arguing about who would be worse for Canada," Jagmeet Singh, leader of the third-placed New Democrats (NDP) and in prime position as a kingmaker, responded, later describing Trudeau and Scheer respectively as "Mr. Delay and Mr. Deny" on climate change.

It was a difficult night for Scheer after a tough few days. Last Wednesday he struggled in a French-language debate – French is the primary language in the province of Quebec, which accounts for 78 of the 338 seats in the House of Commons.

The Conservative leader was then forced to admit newspaper reports claiming he holds dual Canadian-U.S. citizenship were true, raising questions as to why he had hidden the issue in the past.

And in Monday's debate Scheer found himself in the crosshairs, with his repeated allegation that Trudeau was a "fraud" blunted by attacks he faced from other candidates.

Scheer was targeted on his tax plans by former Conservative colleague Maxime Bernier, who now leads the People's Party of Canada, while Green leader Elizabeth May hit out at his plan to cut foreign aid as well as his stance on climate change and abortion rights. 

Yves-Francois Blanchet, leader of the Bloc Quebécois, also criticized Scheer over his approach to the contentious Bill 21: A law which forbids new public service hires in Quebec from wearing religious symbols.

With the race so close, debates take on greater importance – over the coming days the polls will be closely watched to see if Monday's sparring has made a difference ahead of another French-language debate on Thursday. 

The CBC aggregator shows a clear upward trend for Trudeau's Liberals with Scheer's Conservatives flatlining but not falling. With the margins so fine, reaction to the performances of other party leaders could be pivotal in shifting that dynamic. 

With two weeks of campaigning remaining, Canada's election is in the balance: either the Liberal or Conservatives could still walk away as the majority or biggest party.