Supporters of former Conservative cabinet minister Peter MacKay are laying the groundwork for a possible leadership bid in the event party leader Andrew Scheer is unable to defeat the Liberals in the Oct. 21 general election.

Veteran Conservative Party insider John Capobianco, a senior vice-president at the public relations and marketing agency FleishmanHillard Inc., confirmed to The Globe and Mail that friends of Mr. MacKay have discussed the possibility he could seek the leadership if Mr. Scheer falters.

Mr. Scheer would face an automatic leadership review in 2020 and senior players in the Conservative Party, to whom The Globe has granted confidentiality to speak about sensitive matters, say he would have difficulty holding on to the top job if he can’t lead the party to victory at a time when many loyalists believe Liberal Leader Justin Trudeau is electorally vulnerable.

Mr. Capobianco and other Conservatives reached by The Globe stressed that no one is trying to undercut Mr. Scheer’s leadership, and that Mr. MacKay and his supporters are working hard to elect a Conservative government on Oct. 21.

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“He has been extremely supportive of Andrew. He has gone to everybody’s fundraiser that he has been asked to go to. He has done TV … so we are all in for Andrew and we all want him to win,” Mr. Capobianco said in an interview. “But if something happens, who knows, but I think Peter would always be someone that people would say: ‘Hey look, this guy is not done and gone if there is ever a chance that something might happen down the road.’ ”

Mr. MacKay, who was campaigning with candidates in Montreal when he was reached by phone on Tuesday night, said he is not aware of Conservatives organizing on his behalf.

“No, I’m not [aware], and I’m doing everything I can to help Andrew and support him and his team. I’m not entertaining that at all,” he said.

Asked if he has heard from anyone on this issue, he said: “I haven’t – not a soul.”

Mr. Scheer will release a fully costed platform on Friday in Vancouver. He told reporters on Wednesday the platform will include a path to balancing the books within five years. Economists have suggested his promises to date would lead to a $15-billion deficit in 2024-25.

Mr. Capobianco said he has told people that if Mr. Scheer’s party does not form government, they should consider Mr. MacKay as a future leader. Public opinion polls currently show the Conservatives and Liberals in a virtual tie.

“Because it is so tight now, nobody would ever be considering doing anything at this stage,” he said. “He [MacKay] would probably be an alternative for sure if there was ever a leadership race. I don’t even know if Peter would go in because he has [to talk] to his family, to be honest, but there are a lot of people who would love to have him, but it is so premature from that perspective.”

Mr. MacKay, a partner in the Toronto law firm Baker McKenzie, is popular in Conservative circles. He served in the Harper government in justice, defence and foreign affairs from 2006 to 2015.

He was leader of the Progressive Conservative Party until he and Stephen Harper negotiated a merger with the Canadian Alliance in 2003. This led to the formation of the Conservative Party of Canada, ending a decade of vote splitting on the right.

Mr. MacKay was expected to seek the leadership after the Harper government’s defeat, but said in 2016 the time wasn’t right for his young family.

A party insider with close ties to Mr. MacKay, who would not speak publicly about his friend’s future, said the long-time Nova Scotia Conservative is trying to maintain a high profile in case the Conservatives lose and Mr. Scheer fails a leadership review.

It’s not unusual for party leaders to be challenged after elections. Brian Mulroney organized a leadership run after Joe Clark’s Tories lost the 1980 election, and Jean Chrétien did the same in the Liberal Party against John Turner in 1984 and 1988. Mr. Chrétien faced challenges from Paul Martin in the last years of his mandate. Many Liberals see senior cabinet member Chrystia Freeland as a potential replacement for Mr. Trudeau.

Mr. MacKay left the door open to a return to politics when he announced his retirement in May, 2015, and in interviews since.

He said he campaigned in five ridings on Tuesday in Montreal – where the Conservatives have not won a seat since 1988 – calling it “quite a sprint.” He said he went to gatherings at candidates’ headquarters, public meet-and-greets and knocked on doors, and had just arrived at the airport after a fundraising dinner.

Since the summer, Mr. MacKay has crisscrossed parts of Canada for party events.

Bob Plamondon, a political historian with deep knowledge of the Conservative Party, said he frequently hears from people about Mr. MacKay’s potential.

“It’s certainly something that I often hear, and to a large degree, it’s because they look at whether he is someone who can make the party strong and relevant in all parts of Canada,” he said, adding: “Among people who follow politics more generally, a lot of talk about Peter MacKay as an extraordinarily attractive candidate and a potential future prime minister.”

Mr. Plamondon said Mr. MacKay has maintained his profile by engaging in media interviews and talking about foreign policy, and helping to support candidates.

“I think that this is Andrew Scheer’s election to win or lose – and my sense is that Peter is giving him every opportunity to win,” he said.

Mr. Plamondon said two years ago that most political observers would assume Mr. Trudeau would be Prime Minister for at least two terms because majority governments are rarely defeated after one term. But he said no one could have predicted Mr. Trudeau’s missteps.

"The expectation is the Conservatives should win this time out, and if Andrew Scheer does not, if he hasn’t exhibited a lot of growth and potential and a positive performance on the campaign, then I think he’s vulnerable,” he said.

Mr. Plamondon said the revelation of Mr. Scheer’s dual citizenship in mid-campaign was a “jolt to party members” and that he should have dealt with the issue sooner. Mr. Scheer also came under a lot of predictable criticism, he added, for his social conservative views.

“He seems to have been slow to own up to them and to frame how they would characterize his stance should he become prime minister, and he sounded almost Stephen-Harper-like – inauthentic and not as open about his views. If those are his views, he should say ‘that’s what I think’ and not skirt around them.”

With a report from Marieke Walsh

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