For the second time in as many weeks, Privy Council Clerk Michael Wernick will appear before the House of Commons justice committee on Wednesday to testify on the SNC-Lavalin scandal that is roiling Prime Minister Justin Trudeau’s government.

During his first appearance before the committee, Canada’s top public servant – who has served for nearly three decades under both Liberal and Conservative governments – raised eyebrows when he expressed concern about the prospect of political assassinations and the “vomitorium” of social media.

He added that neither he nor anyone in the PMO inappropriately pressured former-attorney general and justice minister Jody Wilson-Raybould to interfere in the prosecution of SNC-Lavalin. Rather, discussions about the future of the Quebec-based engineering and construction giant were “lawful advocacy.”

But Wilson-Raybould directly implicated him in her Feb. 27 testimony, alleging that he was one of the officials who made “veiled threats” and asked her to consider what a failure to cut an out-of-court settlement with SNC-Lavalin would do to the Liberal Party’s political fortunes in Quebec.

The scandal has brought the clerk of the Privy Council out of the shadows and into the limelight, particularly as calls for his resignation have mounted.

It has also focused attention on the unique relationship between a Privy Council clerk and a prime minister – one that the Gomery Commission report, which investigated the sponsorship scandal, described in 2006 as a relationship “not duplicated elsewhere in the government.”

What does the clerk of the Privy Council do?

Unlike the very first Privy Council clerk, who was appointed in 1867, today’s clerks wear three hats. They are at once the secretary of the cabinet, the head of the non-partisan public service or Privy Council, and the deputy minister to the prime minister.

The amalgamation of the three roles is the result of reforms implemented by Prime Minister Brian Mulroney between 1989 and 1993.

“No one should underestimate the importance of the power of the appointment,” the Gomery Commission report states.

The clerk provides non-partisan advice to the prime minister and cabinet on matters of national and international importance, such as who should be promoted to cabinet, and is also responsible for ensuring that the decision-making processes of cabinet function like a well-oiled machine.

That means that the clerk has regular interactions with the prime minister, members of the PMO and the cabinet. Sometimes, this creates overlap in the work of the PMO and the PCO, but “the world of purely partisan politics” is one that the Gomery Commission said the PCO should “intuitively” avoid.

That doesn’t mean that it always does. That same report noted that there is growing evidence that the political PMO and the non-partisan and administrative PCO “seem to be merging more and more into each other,” particularly as more power has shifted to the PMO.

Accordingly, it recommended that the clerk be asked to wear fewer hats. The sole role of the clerk should be to represent the public service to the prime minister and the cabinet, it said.

Charlie Angus, NDP MP and ethics critic, wrote in an open letter to Trudeau that Wernick “overstepped his role” and morphed into a “clear political actor” when he allegedly asked Wilson-Raybould to urgently intervene in the SNC-Lavalin prosecution because of the upcoming provincial elections in Quebec.

Who is Michael Wernick?

Wernick, who is 61 years old, was promoted from deputy Privy Council clerk in January 2016, after serving a number of senior roles since joining the federal public service in 1981.

For eight years, he was deputy minister of Aboriginal Affairs and Northern Development, where he helped oversee a settlement for residential school victims and tried to reform First Nations education.

Since his promotion, Wernick has made mental health in the workplace a priority in the performance contracts for all deputy minsters. In 2016, he announced that a portion of the performance pay for deputy ministers will be tied to how well their department are nurturing a healthy workplace.

Last year, Wernick’s son Paul spoke publicly about his struggles with mental illness and his suicide attempts as a staffer on Parliament Hill.

Trudeau has asked Canadians to believe Wernick’s version of events and described him as “an extraordinary public servant who has served this country and continues to service this country under governments of different political stripes with integrity and brilliance.”

The SNC-Lavalin affair is not the only one in which the PCO has been accused of political interference in a criminal prosecution. Earlier this year, lawyers for Mark Norman, a Navy vice-admiral who is accused of leaking shipbuilding contracts, alleged at a pretrial hearing that the PCO had gone around the justice minister to discuss trial strategy directly with federal prosecutors.

Federal prosecutors have denied those claims.