As the NDP leadership debate got underway in Halifax Sunday, it was clear the NDP candidates were unified in making Prime Minister Stephen Harper their main adversary, and not one another.

The majority of candidates used their opening statements as an opportunity to take aim at Harper and his government's policies.

Peggy Nash compared Harper's vision for families to the American comedy sitcom Leave it to Beaver, while Nathan Cullen said Harper's government presented "a clear and present danger" to Canadians.

Niki Ashton, Thomas Mulcair and Brian Topp alluded to Harper's speech in Davos, Switzerland earlier this week.

Harper's comments on the Canadian Pension Plan, and subsequent memos by his office on future changes to Old Age Security, fuelled the debate.

Ashton and Mulcair called it "an attack" on families and Canadian values, while Topp said Harper was "kicking families in the shins."

Cullen, Mulcair defend positions

The first NDP leadership debate, which was held in Ottawa, was void of any major disagreements between the candidates so on Sunday moderator Dan Leger of The Chronicle Herald said he wanted to see a "distinction" in their positions.

Nathan Cullen's proposal to hold joint nomination meetings with the Liberals and the Greens in ridings currently held by the Conservatives provided a handful of the candidates with that very opportunity.

Martin Singh, Mulcair and Nash all took exception with Cullen's proposal.

Mulcair asked Cullen why the party should "shoot for the bronze medal" while Nash pointed to the NDP's historic breakthrough in the last federal election and warned Cullen not to look "in the rear view mirror."

Cullen defended himself by saying his ultimate goal was to oust the Conservatives, and changing the current voting system, which he said is "broken and flawed" to a more "progressive mixed member proportional system," would be one way to do that.

Cullen was not the only candidate on the defensive.

Paul Dewar asked Mulcair to clarify his position on banning the sale of bulk water, something Mulcair seemed to dismiss at first but answered anyway.

"No one has fought harder to preserve our natural resources from private interests than I have," Mulcair said firmly. But Dewar asked the question a second time.

"I told you I am in favour of protecting our water resources and I am opposed to bulk water exports. But you know that that's my position," answered a visibly annoyed Mulcair.

Mulcair served as the provincial minister of sustainable development, environment, and parks in the cabinet of Quebec Premier Jean Charest until his resignation in 2006.

After the debate, Dewar said he was simply looking for clarity.

While the theme of this debate was "Moving Canada Forward: Giving Families a Break," most of the questions were "based on the most popular issues we received through the website," said NDP interim deputy national director Sally Housser.

The eight candidates vying to replace the late Jack Layton are Niki Ashton, Nathan Cullen, Paul Dewar,Thomas Mulcair, Peggy Nash, Romeo Saganash, Martin Singh and Brian Topp.

The next NDP leadership debate will be in French on Feb. 12 in Quebec City, followed by another three debates in Montreal, Winnipeg and Vancouver.

A new party leader will be chosen on March 24 at a party convention in Toronto.

Layton died of cancer last August, after leading the NDP to a historic win with 103 seats and official Opposition status for the first time.