Former prime minister John Turner says the once-mighty Liberal Party must rebuild from the bottom up and the middle out – and he believes Justin Trudeau is a solid contender to lead the charge.

Turner, who served in various cabinet posts including the justice and finance portfolios, led the Liberals for six years and served briefly as prime minister in 1984. At 38 years old, he was younger than Justin Trudeau is now when he made his first run for the leadership against Pierre Elliott Trudeau.

Liberal MP Justin Trudeau looks on as the Liberal caucus listens to leader Bob Rae speak with the media on Parliament Hill June 14. (Adrian Wyld/Canadian Press)

"Justin Trudeau's a legitimate candidate," he told Evan Solomon, host of CBC News Network's Power & Politics, adding that the young politician will still need to prove his worth in a fair contest. "It's hard to evaluate. He'll have to prove himself in an open leadership convention – as will others."

Turner is optimistic the Liberals can reinvigorate and rebuild – despite past divisions and lingering scars from the sponsorship scandal.

"We as Liberals knew what we stood for: we were fiscally conservative and socially liberal. We were a party that embraced the middle of the political spectrum with very specific ideas," he said. "What we need now is a revitalized policy, a new generation in political ranks and in Parliament. We need a strengthening of our riding associations – at the riding level, not imposed by leadership."

His advice to the next leader?

"Build from the bottom up, not the top down," he told Solomon.

But as Turner remains hopeful for the future of the Liberal Party, he's less enthused about the state of parliamentary democracy in Canada. He's lashing out at an erosion of the system – most recently reflected in the government's omnibus budget implementation bill.

"This omnibus bill surrounded the budget – you couldn't even see the budget anymore. It was an attempt to smuggle a lot of legislation under the feature of the priority of the budget," he said.

"It wasn't parliamentary, it wasn't democratic. It didn't allow for good debate. It didn't allow for questions and answers. It was just demagoguery under the guise of a parliamentary institution called the budget."

The omnibus budget implementation bill, which raises the age of Old Age Security, revamps the rules for Employment Insurance and overhauls fisheries and environmental assessment regimes, is expected to go to the Senate Wednesday.

While Turner conceded the erosion of parliamentary democracy has evolved over time, he insists control has never been as strong or as centred as under Prime Minister Stephen Harper.

"It is not helpful to parliament – in fact it is harmful and therefore harmful to our democracy," he said.