Donald Bayne told reporters that emails show Duffy's living expenses were approved again and again by the Senate's Conservative leadership until the expense controversy blew up and Duffy was forced by the Prime Minister's Office to accept a deal to repay his expenses.
But Harper offered no new information to address the claims by Bayne that the PMO coerced Duffy into taking money from Nigel Wright, Harper's then-chief of staff, and orchestrated the government's response to the allegations against him.
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The RCMP are investigating Duffy over his housing expense claims. Duffy maintains the claims were legitimate and Bayne said Monday that they were approved by Marjory LeBreton, who was the Conservatives' leader in the Senate until last spring.
Harper faced questions from opposition MPs for the first time since the summer break in mid-June and since he signed a tentative trade deal with Europe last week.
However, both opposition leaders were missing from the House, leaving their deputy leaders to ask the lead questions.
The NDP's Megan Leslie kicked off by asking whether Harper could "confirm that his office threatened to kick Mike Duffy out of the Senate if he didn't go along with their scheme."
Harper repeated what he's said every time he's been asked about the allegations in the ongoing Senate expenses scandal.
"We've been very clear that we expect all parliamentarians to respect the letter and the spirit" of the rules, Harper said.
Harper then raised the Canada-EU trade deal and suggested the NDP are opposed.
"On the big issues they're wrong," Harper said.
With Nov. 25 now byelection day in two traditional but vulnerable Liberal strongholds in Montreal and Toronto, the NDP is keen to burnish its credentials as a government-in-waiting at Trudeau's expense.
Voters will also go to the polls in the staunchly Conservative Manitoba ridings of Provencher and Brandon-Souris, but the focus is likely to be on Toronto Centre and Montreal's Bourassa — formerly the stomping grounds of Bob Rae and Denis Coderre, respectively.
Trumpeting the trade deal
As expected, Harper was basking Monday in the triumphant glow of Canada's new deal with Europe, a win custom-made for the new Conservative attack slogan: while we support free trade, the NDP supports "no trade" and the Liberals support "the drug trade" — a dig at Trudeau's support for legalizing marijuana.
Despite the oppositions Senate questions, Harper and his ministers seemed relaxed and laughed easily in the House of Commons Monday.
Trade Minister Ed Fast, Foreign Affairs Minister John Baird and Minister of State Maxime Bernier began banging the free-trade drum Monday with an event in Ottawa spelling out "the next steps ... to ensure all Canadians have the facts" about the agreement and its benefits.
That message isn't likely to drown out the din from the Senate for long, however.
Senator Pamela Wallin is fighting mad at the upper chamber's efforts to suspend her without pay, along with disgraced former Conservative caucus colleagues Mike Duffy and Patrick Brazeau.
Wallin's lawyer, Terrence Sullivan, calls the suspension motions "a fundamental affront to Canadian democracy" that fly in the face of the Senate's own rules.
Mulcair, for his part, was at a morning news conference in Quebec City before an afternoon speech to delegates at the national convention for the Canadian Union of Public Employees. NDP MPs Manon Perreault and Mike Sullivan will also get together in Ottawa today to talk about protecting people with disabilities.