Ontario Premier Kathleen Wynne testifies today in the bribery trial of one of her closest aides and another Liberal organizer, an event that makes political history in the province and could have an impact on the election next June.

The opposition parties are calling it "unprecedented" for a sitting premier to be called as a witness in a political corruption case, and no historians are jumping in to say they're wrong.

While Wynne is not on trial in the case being heard in Sudbury, Ont., the political stakes for her are high.

"She is going to have to be careful, she is going to have to try to be calm and try to be above it all, and if she can to make sure any evidence is deflected far away from her," said political scientist Jon Pammett of Carleton University, in an interview with CBC News.

"These allegations of bribery go to the heart and the highest part" of Wynne's Liberal organization, said Patrick Brown, leader of the Official Opposition Progressive Conservatives, at the legislature on Tuesday.

Pat Sorbara, former deputy chief of staff to Premier Kathleen Wynne, leaves court in Sudbury on the first day of her trial for bribery. (Yvon Theriault/Radio-Canada)

Pat Sorbara, formerly Wynne's deputy chief of staff, and Gerry Lougheed Jr., a prominent Sudbury businessman and Liberal fundraiser, are charged with bribery under Ontario's Election Act. Both pleaded not guilty when the trial began last Thursday in front of Judge Howard Borenstein at the Ontario court of justice.

They're accused of offering a job to induce Andrew Olivier to withdraw his Liberal candidacy in a 2015 byelection. The party brass wanted Olivier to make way for Glenn Thibeault, who defected from the federal NDP, won the byelection for the Liberals and is now the province's energy minister.

Sorbara is also charged with a second count of bribery, accused of offering Thibeault incentives to become a candidate.

If convicted, the maximum sentence is a fine of $5,000, unless the judge finds the accused committed the offence knowingly, which ups the maximum fine to $25,000 and could mean a jail term of up to two years.

"It is relatively rare to see a trial that is so intimately connected with partisan political processes," said veteran lawyer David Butt.

Gerry Lougheed Jr., a prominent Sudbury businessman and local organizer for the Ontario Liberal Party, is also charged with bribery. (Yvon Theriault/Radio-Canada CBC)

When the accusations first came to light in early 2015, Wynne rejected the notion that the Liberals did anything wrong. She kept Sorbara on staff during the ensuing police investigation and named her campaign director of the Liberal Party's 2018 re-election effort. Sorbara resigned that post when charged last December.

Since then, Wynne has declined direct comment on the case, so her testimony is highly anticipated.

"I've been very open with the legislature, I've been open with the media and with the public about the allegations related to the Sudbury byelection," Wynne said in question period on Monday. "I've said all along that I would be open and transparent and that I would work with the process, and that is exactly what I have been doing."

"There are a lot of unanswered questions," NDP Leader Andrea Horwath told reporters Tuesday at the legislature.

"I would hope that the premier starts coming clean, for Ontarians to see exactly what role she played as the premier and the leader of her party in what has become a rather odious scandal."

Wynne is called as a Crown witness. After answering questions from the federal prosecutor in the case, she will find herself in the potentially awkward situation of being cross-examined by lawyers defending two loyal Liberals.

Andrew Olivier was the Ontario Liberal candidste in the 2014 general election and wanted to run in the 2015 byelection. The case hinges on whether two prominent Liberals offered Olivier a bribe to make way for Glenn Thibeault. (Yvon Theriault/CBC)

As a longtime politician, Wynne is accustomed to parrying tough questions from reporters in news conferences and enduring the daily theatrical grilling of question period. It's another thing to get cross-examined by the likes of Brian Greenspan, lawyer for Sorbara.

"It's always interesting, when you have a trial that is at its base about political activity, to watch how politicians will or will not perform well in the very different communicative forum that is cross-examination," said Butt.

'The premier wants to talk to you'

The key pieces of evidence in the case are recordings that Olivier made of conversations with Lougheed and Sorbara in late 2014. He is a quadriplegic and tapes conversations as a way of taking notes.

"The premier wants to talk to you," Lougheed is heard saying to Olivier on one tape. "They would like to present to you options in terms of appointments, jobs, whatever, that you and her and Pat Sorbara could talk about."

In another recording, Sorbara talks to Olivier about "a full-time or part-time job in a [constituency] office, whether it is appointments to boards or commissions."

Olivier also spoke to Wynne, but has testified that he didn't record that call because of technical difficulties.

Wynne's testimony is due to begin at 9 a.m. and is expected to wrap up within the day.