She heads the judicial branch and is the chief justice of Canada, not just of the Supreme Court, and is a member of the Privy Council.
But McLachlin is also the deputy governor general, and if the Governor General were to become incapacitated, she would take his place.
When Gov. Gen. Jules Léger had a stroke in 1974, Chief Justice Bora Laskin replaced him for about six months, handing out medals and reading the speech from the throne.
It's a largely ceremonial role, but when Harper prorogued Parliament in 2008 fearing a vote of non-confidence from a coalition of the Liberals and the NDP supported by the Bloc Québécois, he had to seek permission from Gov. Gen. Michaëlle Jean.
Yet when McLachlin advised Justice Minister Peter MacKay about a potential constitutional issue over the appointment of a Federal Court judge to represent Quebec, the government reacted as if she were an ordinary judge who had behaved inappropriately.
Quebec, because it has a unique civil law code, can only be represented on the Supreme Court by a Quebec lawyer of 10 years' experience or a Quebec provincial judge.
MacKay told the House of Commons on Monday, "neither the prime minister nor I would ever consider calling a judge before a matter that is or could be before the courts."
Adam Dodek, who teaches law at the University of Ottawa and who has written two books about the Supreme Court, said in an interview, "It is completely normal for the executive who is appointing judges to consult with the chief justice of the court."
Government ignored McLachlin's warning
Despite McLachlin's warning about the eligibility of a Federal Court judge representing Quebec, MacKay made it clear the government ignored it.
"We took the position that we were proceeding in not only a constitutional manner, but on the advice of considered learned advice from two former Supreme Court justices and the foremost legal expert when it comes to the Constitution of our county," he said in question period.
The three advisers hired by the government — retired judges Ian Binnie and Louise Charron and lawyer Peter Hogg — gave the green light about appointing a Federal Court judge, although only Binnie's report was released.
In question period, NDP Leader Tom Mulcair inquired whether MacKay is "a henchman of the prime minister's in this unwarranted, unprecedented attack on the Supreme Court and its chief justice."
Dodek can't recall a time in history when a government has been critical of the actions of a chief justice.
McLachlin is a unique head of the top court, the first woman appointed to the post and the longest sitting in history.
25 years on the Supreme Court
The accusation that she inappropriately tried to talk to Harper occurred just a month after her 25th anniversary as a Supreme Court judge. On March 30, 1989, Prime Minister Brian Mulroney appointed McLachlin, an Albertan, to sit on the top court bench.
In 2000, Prime Minister Jean Chrétien made her chief justice. Her retirement date is five years away.
In the past 14 years, McLachlin has changed the court. According to Dodek, she has shortened the court's once notoriously long decision-making times.
"Under Chief Justice [Antonio] Lamer and his predecessors it was not uncommon for judgments to take over a year," he said. Under McLachlin, the time frame is more likely to be six months.
A consensus-building court
McLachlin also brought about a consensus-building court that often delivers unanimous decisions. In a televised interview with host Peter Mansbrige for the CBC's One on One, she spoke of free-for-all debates by all the judges about the cases before them.
They "hash it out," and she always speaks last. "My vote is worth no more than anyone else's."
She said the approach allows her to pick up bits and pieces on different issues. "I can listen to what everyone has to say and sometimes you can pick up different threads, and some of the things dividing people are very small."
Dodek said her court is seen is seen as "a very collegial court," with "an open and co-operative working environment."
He said 4-5 split decisions have been rare in McLachlin's court. "In the U.S they are the rule," he said.
McLachlin, who told Mansbridge it was her goal to make the court more transparent, also brought television cameras into the Supreme Court chamber.
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