Maxime Bernier knows what it's like to be a politician under scrutiny.

The four-term Conservative MP from Quebec, now running for the leadership of his party, resigned as minister of foreign affairs in 2008 after it was revealed that he left classified documents at the house of his then girlfriend – who happened to have past ties to organized crime.

But when he assesses the current controversy surrounding Foreign Affairs Minister Stéphane Dion's approval of a $15-billion Saudi armoured vehicle deal, which began under the previous Conservative government, Mr. Bernier feels no sympathy.

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"He lost a lot of credibility," he says of Mr. Dion over a lunch of warm vegetable salad on a downtown Ottawa patio. "Tell Canadians that you don't like the deal so you won't go ahead, or you like the deal and you're going ahead."

What about Mr. Bernier, who prides himself on the conviction of his principles?

"Because of what's happening right now in the news and all that, I think it's good to do a review," he says, referring to reports of the Saudi government using armoured vehicles to suppress internal dissent.

After a pause, he answers: "I think I won't go ahead with that deal."

Although his own time as foreign minister didn't end how he had hoped, Mr. Bernier says he has taken responsibility and moved on – even laughing at the political cartoons that still poke fun at his misfortune.

After his resignation, he spent three years on the back benches. He was one of only five Conservative MPs from Quebec to survive the 2011 election, and was brought back into the cabinet, albeit in a minor role as minister of state for small business and tourism.

"What I learned is very simple," he says. "Being more cautious with confidential documents."

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Mr. Bernier, a spry 53-year-old who ran a 100-kilometre ultramarathon three years ago for charity, is the second Conservative thus far to declare for the Conservative leadership. MP Kellie Leitch has also thrown her hat into the ring. MP Michael Chong will make an announcement Monday on "the future of the Conservative Party."

The leadership vote itself doesn't take place until May 27, 2017 – and the marathon runner is taking the long road.

On Sunday, Mr. Bernier will officially launch his campaign in his riding of Beauce, where he will hand out free St-Hubert chicken at a local arena. It's reminiscent of the time he hand-delivered Quebec-made Jos Louis cakes to the troops in Afghanistan. Which, he points out, he paid for himself. "It cost me a thousand bucks," he says.

Mr. Bernier says he came to his decision to be one of the first leadership contenders out of the gate to replace former prime minister Stephen Harper after travelling the country and assessing his support.

The self-described "free-market guy" who favours small government and low taxes, and is highly critical of Prime Minister Justin Trudeau's "socialist" deficit spending, has a loyal following in Quebec and Alberta and is well versed in the language of political fundraising.

"I know that I have an organization all across the country," he says. (Whether he will come up with another spectacularly anachronistic jingle, as he did during the 2015 election campaign, remains to be seen.)

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He expects more Conservatives to declare their candidacy by the fall, with potential candidates rumoured to include MPs Jason Kenney, Tony Clement and Lisa Raitt, along with former cabinet minister Peter MacKay and maybe even reality TV host Kevin O'Leary.

While he is well known within the party, Mr. Bernier recognizes that he still isn't a household name in English Canada. And what if the unilingual Mr. O'Leary decides to run? "I'm waiting [for] the time to have a debate with him in French," he says, with a smile.

Mr. Bernier says his leadership campaign will include regular speeches and policy announcements focusing on four themes: individual freedom, personal responsibility, respect and fairness. He also supports some of the socially liberal policies to be debated at the Conservative convention later this month in Vancouver. "I think we must say yes to gay marriage," he says.

For Mr. Bernier, fairness means abolishing subsidies for big businesses – such as Quebec aerospace firm Bombardier.

He's also a pipeline proponent who wouldn't tolerate meddling from provincial or municipal politicians, including Montreal Mayor Denis Coderre, who is opposed to the Energy East pipeline.

"It is not his jurisdiction," he says. "I won't take the phone and call him, it is not his business."

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Perhaps most controversially in his home province, Mr. Bernier says he is reviewing his previous support for supply management – the tightly regulated system that protects Canada's dairy and poultry farmers from most imports.

"I will have a position, and people will judge me with that position after, if I'm a real principled politician or not," he says. "And I know that."