The Canadian Forces veteran who was poised to run for the federal Liberals in the northern Nova Scotia riding of Central Nova has resigned as the candidate over his opposition to Justin Trudeau's support for Bill C-51.

David MacLeod's decision underlines the damage that Mr. Trudeau and his caucus's support for the controversial security bill is doing to the Liberal Party and its brand as defender of human rights.

"It was an integrity-based decision," he said in an interview Monday with The Globe and Mail.

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National opinion polls are showing many Liberal supporters are opposed to the legislation, which Mr. Trudeau and his team helped pass last month. NDP leader Tom Mulcair and his party have been surging in the polls – and some credit that to the NDP's opposition to the bill. Liberal support, according to a recent poll by EKOS's Frank Graves, may be drifting over to the NDP as a result.

Mr. MacLeod served for 27 years in dangerous spots, including Afghanistan, Bosnia and Kosovo. He had planned to take on Justice Minister Peter MacKay, who had previously held the defence portfolio.

But two days after Mr. MacLeod quietly told the Liberal team he was withdrawing, Mr. MacKay surprised everyone with his announcement that he would not seek re-election in the fall campaign.

Mr. MacLeod, who was nominated as the Liberal candidate last fall and has been campaigning hard since, made his decision after watching Liberal MPs support Stephen Harper and his Conservatives in the House of Commons on the final vote.

At first he kept his reasons quiet for fear of rocking the boat, given how sensitive the issue is among Liberals. But earlier this month he sent a letter to Mr. Trudeau, explaining his reasons.

"My resignation as the Liberal Candidate for Central Nova was based on the demands of integrity," he wrote. "The reason for my resignation was Liberal Party of Canada support for Bill-C 51, The Anti-Terrorism Act."

He added that the act is a "very disturbing piece of legislation that undermines Canadian democracy and the Charter of Rights and Freedoms."

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"As a soldier, I helped defend Canada's democracy by participating in peacekeeping, peacemaking and war," he wrote. "Having opposed oppressive political systems in the name of Canadian democracy, I refuse to support any entity complicit in the creation of a repressive act which assaults Canadian liberty."

Mr. MacLeod said that he heard concerns from Liberal supporters in Central Nova about the bill. He said, too, that there was opposition to it from supporters of all the parties.

The Liberals are now searching for a new candidate, and it will be an open nomination, says Kristan Hines, who is part of the Trudeau team in Nova Scotia. "There has been a great deal of interest from potential contestants and there are several individuals from throughout the riding who are seriously exploring their options."

She said that Mr. MacLeod resigned for "personal reasons" and he remains "committed to the Liberal Party and Justin Trudeau."

The bill was introduced in January, partly in response to the terrorism shooting on Parliament Hill last fall. It was extremely popular when it was first revealed – but support for it has fallen considerably since then.

As The Globe's Campbell Clark recently explained, it gives the Canadian Security Intelligence Service (CSIS) broader powers to disrupt perceived threats to national security, the power to get a warrant in secret and to break the law or Charter of Rights as long as the threats don't entail killing, causing bodily harm or sexual assault. There is little oversight.

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He reported that Liberal MPs feared their support for the bill has weakened them and strengthened the NDP, especially in downtown Toronto, Vancouver and Montreal. These areas will be big battlegrounds in the upcoming federal election.

Mr. MacLeod, who has read the entire bill, says that it provides a lot of "opportunity for abuse."

As a candidate, however, he had little say in the actions of the caucus. At first, he had thought the party might find a way around its declaration of support.

"But, they didn't," he said.