As the lawyer for Mike Duffy turned his focus to the Senate rules governing partisan activities, he entered into evidence a photograph of his client and Stephen Harper with a signed note by the prime minister praising the now suspended senator.

The photo, dated June 11, 2009, was signed "To Duff. A great journalist and a great senator. Thanks for being one of my best, hardest working appointments ever." The message was signed "Stephen Harper."

The photo was entered on the third day of Duffy's provincial court trial in Ottawa on fraud, breach of trust and bribery charges. Duffy's lawyer, Donald Bayne, used the photo, which was given to Duffy only five months after he had been named a senator, to make the point that the prime minister was using Duffy for political partisan activities and that taking part in these type of activities was expected of senators.

Partisan activities 'essential'

Not only were such activities expected, Bayne argued, but in fact they are sanctioned by the Senate administration rules that states "partisan activities are an inherent and essential part of the parliamentary functions of a senator."

So if you're involved in partisan activities, Bayne argued in court, then you're entitled to, according to Senate rules, the financial resources and administrative services needed to carry out those parliamentary functions. Of which, he continued, partisan activities are an inherent and essential part. Former Senate law clerk Mark Audcent, who has so far been the only witness to testify in the trial, agreed. 

And what constitutes a partisan activity? Audcent said there is no definition of partisan activities in the Senate administrative rules.

"Partisan activities are not a sideshow in the Senate, They aren't peripheral, whatever the public thinks," Bayne said.

The issue of partisan activities is of significance to Duffy's case as the Crown has accused him of filing Senate expense claims for travel for personal and partisan reasons, unrelated to Senate business.

Bayne told the court that in the Senate expense system, there are virtually no limits on partisan activities eligible for reimbursement. 

The focus on the definition of partisan activities came two days after Audcent was questioned by Bayne about the rules and regulations relating to the eligibility of being a senator and the specific meaning of the words "primary residence."

Definition of primary residence

This is of particular importance to both the Crown and Duffy's defence. Duffy designated his home in P.E.I. as his primary residence, and maintains that's the case, making him eligible to claim meals and living expenses for his time in Ottawa, even though he has lived in Canada's capital since the 1970s. The Crown disputes that P.E.I. is Duffy's primary residence.

Audcent also agreed with Bayne that specific definitions of primary or secondary residences cannot be found in the Senate administrative rules.

Duffy trial: Former Senate law clerk Mark Audcent

Duffy's defence continued their cross-examination of former Senate law clerk Mark Audcent Thursday. (Adrian Wyld/Canadian Press)

While he testified that while there is no one defining criterion within the Senate administration rules that defines residency, there are "indicators of residence." Those include physical presence at the residency, the place where his or her home is and where family lives, and where that individual votes, pays taxes and receives government and health service and has social connections.

Residency is important because, as Audcent explained, the Constitution requires a senator to be a resident of the province he's appointed to represent. Bayne has reasoned that this constitutional requirement therefore made Duffy's residence in P.E.I. his most important residence, and by logical extension, his primary residence.

On Thursday, Audcent said that a letter he gave to Duffy as he was about to become senator included no definition or guidelines on what constitutes a primary residence. Bayne questioned Audcent  about his letter dated Dec. 22, 2008, to Duffy, just before Duffy was to join the Senate.

The letter by Audcent advised Duffy about the duties he must carry out in order to maintain his title, including a "duty to reside at all times in Prince Edward Island."

Asked about the letter, Audcent testified that in terms of residency, there was a difference between being a resident and just owning a home, and that a senator had a duty to be a resident.

This letter.… Is there any definition of residence?" Bayne asked. "No," Audcent said. "There's an invitation to consult."

"Certainly nothing in there about primary residence or any guidelines for that?" Bayne asked. "No," Audcent said.

Brazeau makes appearance

Also at the provincial courthouse on Thursday was suspended senator Patrick Brazeau, who said he came to show support for Duffy.

Brazeau at courthouse to support Duffy1:03

Brazeau has legal issues of his own, facing charges of fraud and breach of trust related to his Senate expenses claims. He had been scheduled for a preliminary hearing in June. That's now postponed.

His lawyer, Christian Deslauriers, told a scrum of reporters that this week's legal arguments around Senate residency rules were of interest to his case. 

Brazeau also has been charged with assault and sexual assault connected with an alleged incident two years ago, and has pleaded not guilty. Testimony began last month in that case.

With files from Kady O'Malley and The Canadian Press