It would be wrong to call the polite opening conversation between the four candidates who have declared their desire to lead the federal New Democrats a debate.

Rather, the event Sunday that marked the beginning of the very long campaign to succeed Thomas Mulcair was an opportunity for the contenders to reaffirm their commitment to NDP values, and to castigate the Liberal government of Prime Minister Justin Trudeau for not fulfilling campaign promises to progressive voters.

All of the candidates – MPs Guy Caron, Charlie Angus, Niki Ashton and Peter Julian – agreed that income inequality is the biggest problem facing Canadians. All agreed on the need for a definitive plan to fight climate change. All agreed that the NDP has to be the voice of workers, immigrants and Indigenous people.

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But these are early days, there are many "debates" to take place between now and the time that party members cast their votes in October, other people could yet join the race, and the tone of the discussion could grow more acrimonious as front-runners emerge.

Perhaps the most important question for the more than 1,000 New Democrats who filled the convention hall and a neighbouring overflow room was about the steps that the candidates would take to make sure the party is ready for the 2019 election. There is much rebuilding ahead for the NDP, which lost more than half of its seats in Parliament when the country previously went to the polls.

Ms. Ashton said she would start a movement for fundamental change that takes pride in being left-wing. Mr. Julian said he would rely on the wisdom of the membership, engage in a massive conversation with Canadians, and reach out to diverse communities and social movements.

Mr. Caron said he would reconnect with the party's base and craft a "precise platform" to campaign upon. And Mr. Angus, whose French was by far the least polished but who managed to keep up with the bilingual format of the debate, said, "We have to go out and we have to do a lot of hard work in reaching people that we haven't talked to before."

All of the candidates spent time reassuring the audience of their NDP credentials. "I am a democratic socialist, an intersectional eco-feminist," Ms. Ashton said in her opening remarks.

Mr. Julian told the crowd, "I bleed orange."

Mr. Caron, who has been an MP for a shorter time than his competitors, pointed out that he began working for the NDP in eastern Quebec in 2002. "Let me tell you, back in 2002, it was actually easier to find a unicorn" than to find a New Democrat in that part of the country, he said.

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And Mr. Angus said the reason he "bought a hundred-dollar suit" and put his name forward was "because the NDP has your back in tough times."

As if to acknowledge the lack of tension on the stage, the moderators asked the candidates to name their best sport, their favourite feminist, their favourite food (Mr. Caron bravely mentioned Cheez Whiz), their favourite musical act, whether they preferred lager or ale and their favourite politician of a different political stripe.

If there was one difficult moment for the four MPs, it was the point where they were asked to explain how they would balance the fight against climate change with the need to keep jobs in a resource-based economy.

Mr. Angus, who said there had to be "hard limits" on the output of greenhouse gas, pointed out that one cannot build windmills without making steel.

But Mr. Julian said "sometimes it's not possible to reconcile the environment and natural resource extraction. When we talk about raw bitumen exports, when we talk about Kinder Morgan and Energy East [pipelines] it is very difficult to reconcile what those projects would mean in terms of accelerating climate change …"

In the end, even if they were not willing to fight each other, the contenders for the NDP leadership were eager to take on the governing Liberals.

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Mr. Caron said that when the 2019 election rolls around, Mr. Trudeau "will be quoting another famous Canadian Justin. He will tell progressives, "Is it too late to say sorry?" – a reference to Justin Bieber's 2015 hit single Sorry.

But Ms. Ashton pointed out that New Democrats have a lot to learn from the way the parties ran their campaigns in 2015. "We played it too safe," she told the crowd. "We let the Liberals out-left us."