Canadian Prime Minister Justin Trudeau’s main rival Andrew Scheer of the Conservatives came out swinging against the incumbent Liberal in an election debate on Monday after a dismal week that saw Scheer blow a previous matchup.

The televised grudge match brought together on stage a record six party leaders.

But the main focus stayed on the two frontrunners who are in a dead heat with only two weeks left before the October 21 ballot. Each is looking to sway a big block of undecided voters.

Scheer went on the attack from the get-go, calling Trudeau “a phoney and a fraud”.

He raised Trudeau’s wearing of blackface makeup, his meddling in the criminal prosecution of engineering giant SNC-Lavalin and his firing of the nation’s first indigenous attorney general “for not going along with his corruption”.

“You do not deserve to govern this country,” he said.

Trudeau shot back, criticising Scheer for his underwhelming climate proposals at a time of global crisis, while defending his record over the past four years in office – including a strong economy, less poverty and low unemployment.

He also accused Scheer and his Tories of fostering “politics of fear and division”.

Scheer, who is untested and relatively unknown after only two years as leader of the Conservative Party, has struggled to endear himself to voters in this campaign.

After being a wallflower in the first debate in French, which he is less comfortable speaking than English, he found himself on the back foot as questions about his dual American-Canadian nationality – revealed only last Thursday – overshadowed his policy announcements.

In cosmopolitan Canada, it is no impediment to high office to have roots in other countries – but Scheer sparked anger by leaving it so late in the campaign to front up with the public.

Critics also highlighted what they saw as a double-standard.

He and fellow Tories in past elections attacked leaders of the Liberals and New Democrats (NDP) as well as former governor general Michaelle Jean because of their dual citizenship.

Questions about his pro-life stance and a 2005 speech in which he assailed gay marriage have also dogged Scheer on the campaign trail.

During Monday’s debate – the only one in English for the three-quarters of Canadians who speak it – NDP leader Jagmeet Singh jumped into the fray, opining: “What we have here is Mr Scheer and Mr Trudeau arguing which is worst for Canada.”

On climate, he said: “You don’t need to choose between Mr Delay [Trudeau] and Mr Deny [Scheer].”

The NDP gained some distance between themselves and the Green Party, led by Elizabeth May, in the race for third place in the latest public opinion polls.

With the latest numbers, if they persist, showing Canadians are likely to elect a minority government, Singh could become kingmaker.

He has said, however, that he would not prop up a Tory government.

The debate also included Yves-Francois Blanchet, leader of the separatist Bloc Quebecois which is on track to regain official party status (needing 12 seats in parliament), and Maxime Bernier, who split with the Tories after a failed leadership run to start the People’s Party.

Singh – an observant Sikh and the first visible minority leader of a federal political party – said Bernier did not deserve to be in the debate because of what he described as repugnant views on immigration and his Twitter attack on 16-year-old climate activist Greta Thunberg, whom Bernier called “mentally unstable”.

“Your ideas are hurtful to Canada,” Singh said, accusing Bernier of “inciting hatred”.

“After a couple of minutes of this debate tonight, I think people can clearly see why you didn’t deserve a platform [to air your views],” he said.