The opposition onslaught against Prime Minister Stephen Harper is on anew in the wake of Sen. Mike Duffy’s explosive Senate scandal speech.

Liberal Leader Justin Trudeau says the only way to restore public faith in the Senate is for Harper to testify under oath about what he knew and when he knew it.

And NDP Leader Tom Mulcair says Duffy has directly implicated the prime minister, who insists he knew nothing of his former chief of staff’s scheme to pay back Duffy’s disallowed housing claims.

Mulcair says Harper has fostered a “culture of corruption” that’s to blame for the expense scandal and the campaign within the Prime Minister’s Office to cover it up.

He says Harper is the common link among 13 different confidantes and advisers named in a CTV report as having knowledge of former chief of staff Nigel Wright’s plan to cut a $90,000 cheque on Duffy’s behalf.

Trudeau, meanwhile, says it’s high time Harper showed some leadership on the file.

Harper has repeatedly insisted he knew nothing of Wright’s intention to foot the bill on Duffy’s behalf until he was told about it in May.

Duffy, for his part, has told the Senate that Harper himself insisted the $90,000 in expenses be repaid, but he stopped short of directly implicating the prime minister in Wright’s repayment.

Today, the focus on the Senate scandal shifts to Sen. Pamela Wallin, who’s expected to defend herself against a motion that she be suspended without pay for her disallowed travel expenses.