As he closes the door on his own Conservative leadership bid for now, Peter MacKay is cautioning other candidates against taking an "offensive" tone that could hurt the Conservative Party's chances in the future.

Mr. MacKay was responding, in general, to questions about proposals put forward by Conservative leadership candidates: by Kellie Leitch to screen immigrants for "anti-Canadian values" and by Tony Clement to enhance security screening of immigrants.

"Having the debate is one thing, but being inflammatory or offensive to any particular … group of people is fraught with danger and long-term brand damage can be the end result," Mr. MacKay said.

Story continues below advertisement

"It's not to say you can't have the discussion, but there is a lot of sensitivity, and as we saw in the election campaign, if you get on the wrong side of these issues and how they're presented, it can cause a lot of harm."

Mr. MacKay didn't go into specifics. But during last year's federal election campaign, the Tories proposed a "barbaric cultural practices" tip line, and former prime minister Stephen Harper suggested the Conservatives would consider banning public servants from wearing the niqab, leading many to criticize the party as wading into identity politics and anti-Muslim policies.

In an interview with The Globe and Mail, Mr. MacKay also said his mother, Macha's, ongoing battle with cancer was a big factor in his decision not to run. He did not want to go into details publicly about her health.

Mr. MacKay, 50, who has two young children with his wife, human-rights activist Nazanin Afshin-Jam, is known to be close to his mother and cited family as his No. 1 priority when he made his final decision last weekend not to run.

But when asked if he believes the party will still be in opposition after the 2019 election, Mr. MacKay didn't rule out running for leadership at a later date. "Am I closing the door or burning bridges for the future? Absolutely not," said Mr. MacKay, now a partner at the Toronto office of global law firm Baker & McKenzie.

So far five candidates have officially joined the race to replace Mr. Harper, with more expected now that Mr. MacKay has made his decision: Ms. Leitch, Mr. Clement, and fellow Ontario MP Michael Chong, Quebec MP Maxime Bernier, and Alberta MP Deepak Obhrai. Conservative MP Lisa Raitt has said her mind is made up on whether to run, but hasn't made her announcement yet. And former Commons Speaker, Conservative MP Andrew Scheer, stepped down from his Opposition House leader duties on Tuesday to explore his own bid. Members will vote on their new leader next May 27.

Mr. MacKay, long perceived as the front-runner, said now that he's out, the race may prove even more exciting.

Story continues below advertisement

"With no clear front-runner, I think it makes the race more competitive and perhaps more interesting to the public, and it will be more a clash of ideas and policy discussion and a chance for people to really showcase what they have on offer," he said.

The former defence and justice minister in Mr. Harper's government said he hopes candidates discuss economic policy, as well as "core Conservative values" such as support for military and veterans, and criminal justice.

"I think having a really fulsome, open debate will also help the party itself revisit some of the raison d'etre for why we're back in opposition, and learn from recent experience and ensure that we're better prepared the next time," he said.

He added that he isn't speaking specifically about any candidates' policies, but in general, "I know there's blowback in areas when you start to look exclusionary."

Mr. MacKay wouldn't comment on whether he has any preferred leadership candidates.

"I'm in a bit of a statesman position now," he said.

Story continues below advertisement

"But I've indicated to all of the people that I've talked to that if I can be of help behind the scenes, and certainly there to bounce ideas off or give them any advice that I might have, I'm happy to do that."