Prime Minister Stephen Harper faced a barrage of hostile questions in the House of Commons today over his former chief of staff's repayment of Senator Mike Duffy's expenses.

At times, Harper seemed shaken under persistent, specific questioning by Opposition NDP Leader Tom Mulcair in particular.

Harper was appearing in question period for the first time since Nigel Wright resigned as his chief of staff amid a deepening Senate expenses scandal more than a week ago.

For 20 minutes, Harper was peppered by short, sharp questions from Mulcair and Liberal Leader Justin Trudeau.

Mulcair, a former lawyer, seemed like a prosecuting attorney, with terse one-sentence questions aimed at Harper as if he were an accused on the witness stand. Again and again, the prime minister was asked what he knew and when he knew it.

When was Harper informed of Nigel Wright's cheque to Duffy? demanded Mulcair. When did he first speak of the matter to Wright? What directives did he give to Wright? And why did it take days for the prime minister to move from complete support of Wright to accepting his resignation?

Time and time again, Harper was on his feet, answering that he only learned of Wright's gift of $90,000 to Duffy on May 15.

Prime minister appeared rattled by questioning

Mulcair asked if Harper had discussed the matter with his former press secretary, Senator Carolyn Stewart Olsen, and if he had raised the issue in cabinet.

Harper said in reply, "The Senate committee has been very clear, it made its own report on these matters, the government’s position is also extremely well-known. Inappropriate expenditures, when people claim expenditures that they never actually incurred, these are inappropriate and must be repaid to the taxpayers."

Mulcair tried the question again, scolding that it was "simple and straightforward." Harper again replied without directly answering whether he'd talked to his cabinet.

"The Senate committee report is a Senate committee report, it is not a matter of government or cabinet business. That is plainly obvious," he said.

Harper, almost expressionless, spoke in a low voice, and at times seemed rattled, once mistakenly saying the word "correct," then quickly changing it to "incorrect," about information Mulcair was presenting in a question.

Trudeau asked every question allotted to the Liberals. He demanded Harper commit to disclosing all documents and emails between Duffy and Wright, as well as a copy of the cheque to Duffy.

Given that the news of Wright's involvement was reported on May 14 on CTV News, the night before Harper says he found out about it, Trudeau asked, "Is the prime minister so unaware of what's going on in his own office that he didn't know about it the night before, when the news broke?"

After question period, Mulcair accused Harper of using Wright as a scapegoat and said the prime minister has an obligation to assume responsibility.

"That's what Stephen Harper is still refusing to do," Mulcair said.