Ontario Finance Minister Dwight Duncan is recalling the time he skipped school back in 1972 and went to a shopping mall to watch Pierre Trudeau give a campaign speech.

Pen and paper in hand, the 13-year-old worked his way through the crowd to the front of the rope line in the Devonshire Mall in his hometown of Windsor, hoping to get Mr. Trudeau's autograph.

Playing hooky marked the beginning of Mr. Duncan's involvement with the Liberal Party. He didn't get Mr. Trudeau's autograph that day. But he became a member of the party during the 1972 federal election campaign and started working as a volunteer for Herb Gray, his local MP.

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Mr. Duncan came of age admiring Mr. Trudeau. Forty years later, he is supporting his eldest son, Justin Trudeau, the presumptive front-runner in the Liberal leadership race.

"For some of us, there's a bit of nostalgia, but it's very much about the future," Mr. Duncan said in a recent interview in his office overlooking the Ontario legislature. "I think the Liberal Party is showing real signs of life right across the country, and I think Justin Trudeau has what it takes to lead the party back."

His involvement with Mr. Trudeau's campaign signals that he will remain active in politics, at the very least as a fundraiser and volunteer, even as he prepares to retire from the provincial scene. He plans to step down from cabinet shortly after a successor to Premier Dalton McGuinty is chosen next weekend. But the 54-year-old career politician is leaving the door open to running federally down the road.

Winning Mr. Duncan's support was a major coup for Mr. Trudeau, according to campaign insiders. As the senior Liberal economic minister in Canada, Mr. Duncan adds gravitas to the younger, less experienced candidate, they said.

Gerald Butts, one of Mr. Trudeau's top advisers and a former principal secretary to Mr. McGuinty, personally reached out to Mr. Duncan. The two had lunch in Mr. Duncan's office shortly after Mr. McGuinty announced his resignation last October. But by then, Mr. Duncan already knew he was predisposed to supporting Mr. Trudeau.

He saw Mr. Trudeau's charisma first-hand when he introduced him to party supporters at an event in his home town. The annual Windsor Essex Liberal barbecue typically attracts about 60 people. But on a Saturday afternoon last September, nearly 500 people flocked to the Ciociaro Club, where many tried to shake Mr. Trudeau's hand and have their photos taken with him.

"We haven't seen that in the Liberal Party since his father was leader," Mr. Duncan said. "People are looking for hope."

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Mr. Duncan said Mr. Trudeau is part of the reason he is considering jumping to federal politics. He is leaving Queen's Park at a particularly difficult time for the minority Liberal government. Mr. McGuinty is stepping down amid controversies over two cancelled gas plants and a standoff with the province's teachers. His right-hand man is following him out the door.

Mr. Duncan will not run for re-election in Windsor-Tecumseh, a seat he has held since 1995. He plans to step down as Deputy Premier and Finance Minister when Mr. McGuinty's successor appoints a new cabinet. Mr. Duncan could vacate his seat even sooner if former cabinet colleague Sandra Pupatello, the front-runner in the provincial leadership race and the candidate he is supporting, becomes the next premier – he will offer his good friend and fellow Winsorite his seat in a by-election.

Already, he is being courted to run for the Liberals federally in the 2015 election. At a recent, $500 a plate fundraiser for Mr. Trudeau at the Liberty Grand in Toronto, Liberal insiders said a campaign team member articulated what many others in the ballroom were thinking when he thanked Mr. Duncan for his speech introducing the candidate.

"I wished him a restful but brief reprieve from public life," Mark Sakamoto, a Toronto lawyer who is helping with fundraising, recalled in an interview. "I said, '2015, that's all I'm saying, Dwight.'"

Mr. Duncan's political career has spanned 25 years, including a stint as a city councillor in Windsor. For someone who counted John F. Kennedy and Martin Luther King as well as Pierre Trudeau among his heroes growing up, it is difficult to imagine him anywhere else but in politics.

In recent years, it is Sir Winston Churchill who has had an enormous influence on him. He sneaked away late at night while attending a conference in London in 2006 to smoke a cigar beside the bronze sculpture of the former British prime minister in Parliament Square.

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Not only did Churchill achieve "enormous greatness," Mr. Duncan said, he had the strength of character to admit, later in life, when he made mistakes.

For his part, Mr. Duncan is not quite ready to take stock of the Liberal government's record. Asked if he thinks the government could have dealt with teachers differently, he demurs, saying he is not going to talk about process.

"I take no pleasure in this," he said. "None whatsoever."