Pity the poor prime minister.

Stephen Harper, pre-disposed as he is to dislike an unreformed and now not-easily reformable Senate, is faced with yet another difficult constitutional question.

He's allowed the 11 vacancies to build up in red chamber — there'll be 17 by the end of the year — and the feeling is he is not all that interested in filling them.

Harper's majority there remains intact and by not making appointments to the now unpopular and scandal-ridden upper chamber, he can avoid having to answer uncomfortable questions about patronage and power, and perhaps, expenses.

But can the prime minister keep holding on? And if so, for how long?

CBC News reported Tuesday Harper is under pressure from Conservative senators to start filling up those empty seats.

They argue work is becoming difficult — not enough senators to fill up committees — and besides that, the regional balance is starting to go wonky: An unacceptable situation in what's supposed to be the House of the Provinces.

But the prime minister has shown no interest so far in meeting those requests and it's not clear he even has to.

Opposition leader Thomas Mulcair argues Harper could turn his back on the Senate and simply walk away, leaving that piece of our Parliament to wane from neglect.

"There's no constitutional requirement to fill them," Mulcair told host Rosemary Barton on CBC News Network's Power & Politics. "We could let the thing die on the vine — just wither away by attrition, name no one else to the Senate."

'Summon qualified persons'

Of course, that fits with the NDP leader's view of the place: That the thing should be abolished. But the prospect of a Senate starved of money, membership and legitimacy would likely not keep with the constitution.

Yes, it's true the prime minister is not by name required to appoint senators, but the constitution does spell out the Governor General's responsibility to ensure qualified Canadians are brought forward as new members.

Section 24 says the Governor General, "shall, from time to time, in the Queen's name, by instrument under the great seal of Canada, summon qualified persons to the Senate." And, as everyone knows, in our system, the GG doesn't do that sort of thing without the prime minister's advice.

Political scientist Emmett Macfarlane argues the imperative placed on the shoulders of the Governor General is, in practical terms, actually a constitutional burden the prime minister must wear.

"I wouldn't say that it is black and white crystal clear that there is an obligation to name senators," Macfarlane said.

But, he says, if you interpret Section 24 in practical terms, it does begin to look an obligation.

The Governor General politically is unable to act without the support of the prime minister. To act on his own would lead to a separate set of constitutional problems that would shake the foundations of Canada's democracy.

Macfarlane argues a long-term refusal by the prime minister to name new Senators for the Governor General to appoint would lead to an inconsistency between constitution and convention that cannot stand.

"I would personally argue that the phrasing in the text speaks of a constitutional requirement to make regular Senate appointments, and I think the conventions certainly speak to that as well," Macfarlane said.

"Whether the Supreme Court would agree with me is an entirely different matter."

A role for the Supreme Court?

Tuesday, former Conservative senator Hugh Segal told CBC News he didn't think there was any obligation to name senators to sit in the 105-member chamber, as long as its membership didn't dip below the quorum of 15 bums in cushy red seats.

Renowned constitutional lawyer and professor Peter Hogg takes a position in line with Segal.

There's no legal obligation for Harper to name new names, Hogg says. But the prime minister could have trouble following that road to its end.

The Supreme Court in the recent Senate reference ruling said the government could not make changes to the Senate that have the effect of amending the Constitution without undertaking a full-blown bit of Constitutional reform.

So, if the Senate was diminished to such a degree that it could not do its work or serve its Constitutional function, then that diminishment would be unconstitutional in itself.

Phew.

It's here Peter Hogg says the Supreme Court might think about beginning to act — but, he says, that would be an extreme case.

"Where the Senate has effectively been abolished by the refusal of the PM to recommend appointments, perhaps that is one instance where the [Supreme Court] might be tempted to grant a remedy," Hogg wrote in an e-mail.

"Not because of a general duty to make appointments, but because the constitution assumes a functioning upper house and the PM by unilateral inaction should not be allowed to effectively amend the constitution."

But, possessed as it's said to be of "neither the purse nor the sword," the Supreme Court would not be able to make those appointments itself. The prime minister technically doesn't make the appointments and the Governor General likely can't be ordered to — so what then?

University of Ottawa political scientist Philippe Lagasse says if by refusing to name so many new senators the prime minister unconstitutionally altered the architecture and operation of Canada's Parliament, the Governor General would be left with no choice.

"The Governor General at that point would effectively recognize that the prime minister of Canada was acting unconstitutionally. If the GG found the PM just totally refused, then he would have grounds to dismiss him."

The nuclear option, one might say.

Where's the guidebook?

It's this sort of conundrum that highlights a failure in the administration of our constitution.

There's been no codification of the conventions that flow from the old and arcane bits of the act.

There are a few key opinions that all Canadians seems to share that offer general guidance — that the Governor General can't willy-nilly start ignoring the advice of democratically elected leaders, for instance, lest our system of government fail, or that the prime minister can't ignore the will of Parliament expressed through a vote, lest our democracy fail. But there are no guidebooks for how the other bits must be run.

Lagasse says there is such a guidebook for the United Kingdom. The Cabinet Manual, as it's called, "sets out the main laws, rules and conventions affecting the conduct and operation," of the government of the U.K. — even defining the relationship between the government, the Sovereign and the judiciary.

Canada, Lagasse says, could use such a book.

In the meantime, you might as well be asking: How many senators can dance on the head of a pin?