The four candidates vying to replace Tom Mulcair as the next leader of the federal New Democrats faced off in Saskatoon on Tuesday exchanging blows over climate change and pensions.

The remaining candidates in the race are Ontario MP Charlie Angus, Manitoba MP Niki Ashton, Quebec MP Guy Caron and Ontario MPP Jagmeet Singh. B.C. MP Peter Julian announced last week he was leaving the race after disappointing fundraising numbers.

The debate opened with the candidates being asked how they would bring outlier provinces such as Manitoba and Saskatchewan into the fold when it comes to introducing a national price on carbon.

Angus said Saskatchewan Premier Brad Wall was living in the past, and was like "the man violently defending the future of the typewriter when everyone else has moved to cellphones."

Ashton said the NDP needs to help create "good green jobs right here in the Prairies."

Jagmeet Singh calls out Brad Wall for 'callous' budget0:36

Describing Wall's recent budget as "callous and savage," Singh said the NDP has to make sure no one was left behind in the transition away from a resource-based economy. That would mean easing the burden of a carbon tax on low- and middle-income Canadians.

Caron said Wall and Manitoba Premier Brian Pallister were simply wrong when it came to their climate change policies.

During a direct exchange portion of the debate, Angus and Singh sparred over how each candidate would reduce poverty for seniors if they were elected prime minister. 

Angus attacked Singh for his proposal to help reduce poverty for seniors by introducing a benefit that combined existing programs into a single benefit that was income-tested.

Angus said the principle that pensions are universal, regardless of income, was a fundamental principle of the NDP.

"Old Age Security is not universal right now so you need to do some research," Singh said. "Right now if you earn over $70,000, its already clawed back so I guess you need to check your facts."

Angus said he would "do the research," but the NDP had to protect Old Age Security and should be making it the party's highest priority.

"Here in Saskatchewan of all places how could you call a means-test redistribution," Angus asked.

"It is, it's the definition," Singh said. "If someone is earning $1 million a year they don't need $1,000 a month. That person should be contributing to people who are living in poverty."  

Jagmeet Singh tells Charlie Angus to 'check his facts'0:33

The candidates were also asked if there should be a change to the amount people can invest in tax-free savings accounts and RRSPs to help them retire with income security.

Angus, describing Finance Minister Bill Morneau as the "privatized pension king of Canada," said he would be the leader the NDP needs to take on the minister in the House of Commons this fall.

Ashton said Morneau made a career out of "screwing peoples' pensions" arguing that her tax reform plan would take on the "rich and powerful" in Canada.

"Yes people are turning to other modes of saving their money, but who's doing most of that? It's the rich," Ashton said. "The benefits of tax loopholes are going to the rich."

Caron said there is no way an ordinary citizen could put aside $26,000 a year for their RRSPs, so Canadians need to be better served by publicly funded pensions so they can retire with dignity.

Public safety

The candidates were also asked how they would keep Canadians safe.

Caron said the NDP had to deal with serious crimes by helping victims not only during the trial process but afterward.

Angus said he would make sure police services across Canada have the resources that they need to keep Canadians safe.

Singh said Canadians have been sold a "false choice" of either being safe or having civil liberties, because Canada could have both.

He said the prison system had to be focused on rehabilitating people while at the same time recognizing there were always going to be some dangerous criminals that needed to be kept separate from the rest of Canadians. 

NDP leadership candidates on supporting Liberals1:18

Principles and power

On the question of how the candidates would balance their principles with political power, Ashton said she was on the side of Indigenous people, workers and farmers and was against corporate greed and policies that make inequality worse.

"Canada might be ready for that inspiring brand of Prairie populism again," she said, promising to challenge "corporate greed."

Caron said the NDP could not abandon rural voters to Conservatives in the effort to fashion an NDP government, saying the party has to work hard to fight for urban and rural Canadians at the same time.

Singh said the NDP had to use the notion of Prairie populism to win government so it could implement policies that would make a difference for Canadians.

Angus criticized Trudeau and said he would bring more substance than style should he be elected leader and then prime minister.

Racking up endorsements

Hours before the debate, two of the candidates, Singh and Caron, announced endorsements from within the party.

Caron is being supported by former Saskatchewan MP Lorne Nystrom, former Quebec MP Rosane Doré Lefebvre and Lia Storey-Gamble, co-chair of the Young New Democrats.

For his part, Singh unveiled the endorsements of eight sitting members in the B.C. Legislature, one former member and two candidates.

Tuesday's debate is the only one being held on the Prairies ahead of the party's October leadership vote.

Watch the full NDP leadership debate:

With files from The Canadian Press