But a Vancouver lawyer will try later this month to force the prime minister's hand.
Aniz Alani is going to court to challenge Harper's refusal to fill 18 vacancies in the unelected upper chamber.
Oral arguments are scheduled to be heard on April 23 in Federal Court.
Alani is asking the court to declare that Senate vacancies must be filled within a reasonable time.
Harper has not appointed a senator since March 2013 — just as the Senate expenses scandal was heating up.
That scandal grew to engulf Harper's government and his inner circle, with three of his own Senate appointees — Duffy, Patrick Brazeau and Pamela Wallin — at the heart of the morass.
Duffy's trial on fraud, breach of trust and bribery charges began this week. Brazeau and former Liberal senator, Mac Harb, are awaiting trial and Wallin remains under police investigation.
More senators could yet get caught up in the scandal when auditor general Michael Ferguson reports in June on the findings of an unprecedented, comprehensive audit of senators' expense claims.
Small wonder Harper, who has appointed 59 senators since 2006, has no appetite for continuing to pack the upper chamber with as many Conservatives as possible.
"I don't think I'm getting a lot of calls from Canadians to name more senators right about now," Harper said late last year.
"From the government's standpoint, we're able to continue to pass our legislation through the Senate. So from our standpoint, the Senate is continuing to fulfil its function."
It was that "fairly glib" response to a question about the vacancies that prompted Alani to launch his court challenge.
"It seems to misunderstand the purpose of the Senate. It's not just to rubber stamp your legislation, it's to provide detailed review of all sorts of proposals," Alani said in an interview Thursday.
"But also, I thought, I don't think you have the choice, I'm pretty sure the Constitution requires you to fill the vacancies when they happen."
Among other things, Alani argues that refusal to fill vacancies leaves provinces with fewer representatives in the Senate than they are constitutionally entitled to.
However, the federal government is urging the court to dismiss the case.
In court documents, federal lawyers maintain it's the governor general's constitutional responsibility to appoint senators, that it's only by convention that the appointments are made upon advice from the prime minister.
They argue that conventions are not enforceable by courts and, in any event, that the Federal Court has no jurisdiction to hear such a case.
Should Alani win, he may actually be doing Harper a favour, giving the prime minister cover to fill the vacancies before this fall's election, while claiming that the court made him do it.
While filling the vacancies would risk the wrath of voters, it would ensure the Conservatives continue to dominate the Senate for years, whether or not Harper wins re-election.
Leaving the seats unfilled would risk immediately forfeiting the Tory hold on the Senate should Harper lose the election.
The Conservatives currently hold 52 of the Senate's 105 seats, the Liberals 30 and Independents five, although three of them are under suspension from the chamber. There are 18 vacancies at the moment, with two more senators due to retire before the election.
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