OTTAWA -- Prime Minister Stephen Harper continues to recast himself in the role of stern disciplinarian in the Senate expense narrative, telling a Halifax radio station he "dismissed" his chief of staff for writing a $90,000 cheque to Sen. Mike Duffy.

Last spring when word of the secret payment first surfaced, Harper initially praised Nigel Wright, before appearing to regretfully accept his top lieutenant's resignation several days later.

"I accept that Nigel believed he was acting in the public interest, but I understand the decision he has taken to resign," the prime minister said last May 19.

Harper is now striking a new tone.

"Look, I think the responsibility whenever things go wrong is for us to take appropriate action," Harper told radio station News 95.7 Halifax in an interview aired Monday morning.

"As you know, I had a chief of staff who made an inappropriate payment to Mr. Duffy. He was dismissed."

At issue is an alleged coverup in which the Prime Minister's Office paid off Duffy so that he could repay disputed expenses, in return for which a Conservative-dominated Senate audit committee would whitewash Duffy's behaviour and make the scandal disappear.

The expense questions were first a matter dismissed by government as a media smear, then a political problem to be quietly managed away.

The latest change in tenor began last week after Harper and his office faced a full-on broadside from Duffy and fellow Harper appointees Pamela Wallin and Patrick Brazeau, who are also mired in their own expenses controversies.

The Senate Conservative majority is pushing to suspend, without pay, all three of their former caucus mates. That threat has brought the Conservative fight into the open.

The prime minister has been extremely reluctant to respond to the Senate imbroglio, more often than not allowing his House of Commons subordinates to parry opposition questions on the matter.

But Harper went on offence last week after Duffy's incendiary address in the Senate chamber, in which he described a meeting between himself, Harper and Wright -- "just the three of us" -- to discuss expense repayment.

"Darn right I told him he should repay his expenses," the prime minister responded the next day in the Commons.

Harper has also come out four-square behind the Senate suspension motions, which were sprung after Parliament returned on Oct. 16 following an extended summer recess.

The prime minister even makes the argument that the long delay in getting to the bottom of the affair -- a delay that has included government stonewalling, continually changing stories and even Harper's decision to prorogue Parliament for a month this fall -- is reason for swift movement now.

"When you have collected hundreds of thousands of dollars in inappropriate expenses and it's taken a year to get to the bottom of this, I think people expect action," Harper told interviewer Jordi Morgan.

The interview was one of three the prime minister recorded Friday with selected radio stations in Toronto, Saskatoon and Halifax. All followed similar formats, with Harper being asked about a European trade deal, the government's throne speech and the troubled Senate.

Morgan, a former candidate and Harper staffer, said the Prime Minister's Office imposed unspecified "conditions" on the terms of the interview.

Some senators have said Duffy, Wallin and Brazeau deserve a full hearing and due process; there are indications that the Senate leadership may move this week to soften the motions.

An RCMP investigation continues into the behaviour of the senators and of Wright. No charges have been laid.

Duffy, Wallin and Brazeau all maintain they did not knowingly fudge their expenses and believed they were following the rules.

But Harper now says it is "crystal clear" that there was a misappropriation of public funds.

"There has been a view in the Senate, a long historic view, and there's a few people who still believe it, even in our party, that the only standard for sitting in the Senate is that you've not been convicted of a crime," he said.

"I'm sorry, that is just not good enough."