The New Democrats amplified their long-standing call to abolish the Senate outright, while the Liberals accused Prime Minister Stephen Harper of showing poor judgment when he vouched for Wallin's expense claims earlier this year.
Liberal MP Stephane Dion and Sen. James Cowan, the party's leader in the Senate, said a pattern of dubious decisions on the prime minister's part is beginning to emerge over the spending scandal in the upper chamber.
Harper told the House of Commons in February he had personally looked at Wallin's travel costs, saying they were on par with other parliamentarians travelling between Ottawa and Saskatchewan.
"In terms of Sen. Wallin, I have looked at the numbers," Harper said at the time. "Her travel costs are comparable to any parliamentarian travelling from that particular area of the country over that period of time."
Dion, the former Liberal leader who is now the party's democratic reform critic, also cited Harper's apparent reluctance to fire his chief of staff, Nigel Wright, for footing the $90,000 bill for Sen. Mike Duffy's own impugned expense claims.
Harper initially defended his chief of staff and insisted he had full confidence in Wright, who nonetheless resigned his position five days after the revelations about the $90,000 cheque first surfaced.
"At first glance, the prime minister should have seen the red flags. It should have raised alarms. Without indeed knowing all the details at first glance, at broad review, he should have seen the problems," Dion said.
"The pattern is repeating itself."
In the latter case, Harper and several ministers insisted that only Wright was aware of the arrangement with Duffy. It has since emerged that three other senior staffers in the Prime Minister's Office also knew about the payment.
As far as his defence of Wallin is concerned, the Prime Minister's Office says Harper was only talking about Wallin's overall travel expenses, not her individual claims.
The Harper government has no choice but to abolish "this institution that was created before we had electricity," said the NDP's Paul Dewar, reprising a long-held New Democrat credo.
"At the end of the day, I think most people understand that this is an institution that needs to be sent packing, period," Dewar said.
"It's not just about the claims and if they're legitimate. It's about, 'Is this body legitimate,' and we don't think it is."
On Tuesday, the Senate called in the RCMP after an audit called into question a litany of dubious travel claims spanning nearly all of Wallin's career as a senator, which began late in 2008.
The auditors flagged $121,348 in inappropriate expenses and called for further review of nearly $21,000 in additional claims.
Wallin — who denounces the audit as "fundamentally flawed and unfair" — has already repaid $38,000, and has since promised to reimburse any disallowed expenses out of her own pocket, with interest.
The Senate, meanwhile, disclosed Wednesday that the price tag for hiring accounting firm Deloitte to audit Wallin's expenses was $126,998 — more than the total Wallin is now required to pay back.
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