WATCH: A former chief of staff to Brian Mulroney and Conservative adviser says Peter MacKay’s departure from federal politics puts his riding in play for the Liberals as the last of the federal Progressive Conservatives makes his exit.

OTTAWA — The unexpected decision from Conservative stalwart Peter MacKay to leave politics has left a string of questions for the party faithful, not least of which is what will happen to the Nova Scotia seat he’s vacating.

“This was a safe seat in an area that’s now being impinged upon by the Liberals,” said David McLaughlin, former chief of staff to Brian Mulroney and adviser to Conservative governments.

“When you have a family name that all of a sudden moves, all of a sudden that seat gets into play. So right now, Central Nova is in play for the Liberals, so that’s kind of worrisome.”

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Another big question is what it means for the Conservatives when one of its founding members, a man who has sat as an MP since 1997, decides to leave.

“After a decade in power, we have people leaving,” McLaughlin said, recalling departures such as John Baird and Jim Flaherty.

“Does this mean we really are a one-trick pony, a one-person government?”

Over time, the merger between the Progressive Conservatives and the Canadian Alliance that gave birth to the Conservatives has become more of a one-person party, McLaughlin said, pointing to what he says has precipitated that view.

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“This party, when it came together, was really formulated on the basis of one thing: unite to defeat the Liberals,” McLaughlin said. “The way they defined conservatism, at its founding meetings in the constitution in 2003, was pretty bland.”

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That blandness, or lack of a defined ideology, afforded Prime Minister Stephen Harper leeway to mold the party to his personal specifications, McLaughlin said.

But the very fact Harper changed his schedule Friday to fly east and speak at MacKay’s resignation announcement signals trouble, said Ottawa Citizen parliamentary bureau chief Mark Kennedy.

“The Progressive Conservative wing of the party is leaving, and I look at that and I look at the prime minister, and he looks like a lonely man these days, as he heads into a campaign.”

READ MORE: As Peter MacKay exits stage right, Liberals eye his Nova Scotia riding

MacKay’s resignation could leave many “red Tories” eyeing the Liberals, said Toronto Star columnist Susan Delacourt.

“We haven’t been watching closely enough how much [Liberal leader Justin] Trudeau is after those people who were Paul Martin Liberals,” she said. “Certainly [the old Progressive Conservatives] would be getting a signal from this MacKay resignation.”

In the wake of Friday’s announcement, party faithful might also ask whether this is truly it for MacKay.

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Could he return with a chance at becoming leader and maybe even prime minister?

There’s a good possibility, McLaughlin said.

“In part because of his successful tenure in politics, but also because of the way he’s leaving now,” he said. “He’s not going to be tagged with whatever happens, good, bad or ugly in October … Given his name recognition, given the fact that he was a leader of one of the two founding parties that brought together this Conservative Party, he’s going to be on everybody’s short list.”