A day before the Mike Duffy trial resumes, with long-awaited testimony expected from star witness Nigel Wright, the Liberal and NDP leaders were quick to throw gasoline on the smouldering scandal.

On Tuesday, Tom Mulcair accused Stephen Harper of trying to “hide in the North Pole” during the trial, while Liberal Leader Justin Trudeau said Ottawa has become a “partisan swamp” under the Conservative leader’s watch.

CTV News has learned that this week, Harper will be travelling to northern Canada.

Wright, the former chief of staff for the prime minister, is scheduled to take the stand this week as the fraud trial of former Conservative senator Mike Duffy resumes Wednesday following a two-month hiatus.

Wright is expected to answer questions related to the $90,000 cheque he gave Duffy to pay back disallowed housing and travel expenses.

Harper addressed the issue at a rally in Markham, Ont., on Tuesday.

“Very briefly, on the issue of expenses, as you know Mr. Duffy admitted this, I told Mr. Duffy I thought he should repay his expenses,” the Conservative leader said.

“But when it came to those expenses that were taken from the Senate that we thought were not proper, I said to Mr. Duffy that he should pay those expenses. I was told that he was going to repay those expenses, and we were all told he had repaid those expenses.”

“When I learned that was not true, I made that information public. And we have taken appropriate actions to make sure that people are being held accountable, and that is what is happening,” Harper said.

Amid questions raised by RCMP documents filed in court that included Wright emails to a lawyer and PMO staff saying the payment had been approved by the prime minister, Harper has denied any knowledge of the cheque being given to Duffy.

On Monday, Harper told attendees at an Ottawa rally that he never told his former chief of staff he was “good to go” with the payment.

Duffy has pleaded not guilty to 31 charges, including fraud, bribery and breach of trust.

In his remarks Tuesday, Trudeau says that a Liberal government would revamp the scandal-plagued Senate by instituting a merit-based appointment process.

“The Mike Duffy scandal is more than just a symbol of Stephen Harper’s poor judgment,” Trudeau told supporters in Papineau, Que. “It represents all that is wrong with Stephen Harper’s Ottawa.”

Speaking with supporters in Mascouche, Que., Mulcair said Harper is known to speak “from both sides of his mouth,” and the Duffy trial is no exception.

“I do find it interesting that Mr. Harper has decided to hide out in the North Pole during the Mike Duffy trial this week. He used to try to hide out from my questions in the House of Commons, but they eventually caught up with him.”

With files from The Canadian Press