When Gerald Butts announced his resignation as Justin Trudeau's principal secretary, his reasoning suggested he feared allegations springing from the then-burgeoning SNC-Lavalin controversy might be a distraction for the prime minister.

"My reputation is my responsibility and that is for me to defend," he wrote in a statement. "It is in the best interests of the office and its important work for me to step away."

The scandal centres around one key question: whether the prime minister and senior members of his team tried to pressure the former attorney general, Jody Wilson-Raybould, to step in and resolve the corruption and fraud case against SNC-Lavalin Group Inc.

This pressure is alleged to have come in an effort to spare the Montreal-based engineering and construction giant from criminal prosecution and potentially save thousands of jobs that could be lost from a guilty verdict. If convicted, the company could be blocked from competing for federal government contracts for a decade.

Now, just over three weeks later, Butts is returning to the political playing field, his apparent act of political self sacrifice seeming to have had no effect on quelling the drama unfolding in Ottawa. As Trudeau struggles to get ahead of the controversy, Butts can only hope his testimony at the House of Commons justice committee will help counter the fallout that has sparked a political crisis within the Liberal government.

Prime Minister Justin Trudeau has faced the recent resignations of two high-profile cabinet ministers over the SNC-Lavalin scandal. (Frank Gunn/Canadian Press)

Indeed, since Butts's departure from Trudeau's inner circle of key aides, the ramifications from this — one of the biggest federal political scandals in years — have continued to escalate. If social media is any indication, the controversy is being keenly observed by the Canadian public.

Based on data shared with CBC News by Twitter Canada, on the day Wilson-Raybould testified, the volume of conversation using the #cdnpoli hashtag was the second highest ever, exceeded only by the October 2015 election.

Hottest ticket

Last week's testimony of Wilson-Raybould before the justice committee was the hottest ticket in Ottawa in recent memory, and certainly since the SNC-Lavalin scandal broke. But Butts's appearance today is a close runner-up. While the committee will hear again from Privy Council Clerk Michael Wernick, and Nathalie Drouin, deputy minister of justice and deputy attorney general, Butts is the main event.

His appearance comes just two days after the shocking resignation of Jane Philpott, a key and highly respected minister, who stepped down from her post as Treasury Board president, saying she had "lost confidence" in how the government has dealt with the SNC-Lavalin case and in "how it has responded to the issues raised."

WATCH | CBC's Salimah Shivji explains what to watch for in Wednesday's testimony

Trudeau's principal secretary expected to bring documents and talk dates before House judiciary committee. 2:17

Butts had informed committee chair, Liberal MP Anthony Housefather, that after watching the testimony of Wilson-Raybould, he believed his evidence "will be of assistance to the Justice and Human Rights Committee in its consideration of these matters."

As principal secretary, Butts remained behind the scenes, speaking to reporters on background but not for attribution. However, he was particularly outspoken on Twitter, where he would engage with, or lash out at critics and journalists, promote and champion the Liberal Party and defend his former boss.

Trudeau has repeatedly stated that he disagrees with Wilson-Raybould's characterization of events, and that he makes no apologies for trying to save jobs. But some Liberal MPs have expressed concerns that Butts, to defend his actions and those of the prime minister, may revert to his attack dog Twitter persona, the ever loyal political servant launching a full throttled counter-attack.

'Categorically' denies political interference

In his resignation statement, Butts "categorically" denied the claims of any attempt at political interference, saying that "any accusation that I or the staff put pressure on the attorney general is simply not true."

On Feb. 27, Jody Wilson-Raybould testified that when she was attorney general, she was pressured by top government officials, including the prime minister, to step in and resolve the corruption and fraud case against SNC-Lavalin. (Sean Kilpatrick/Canadian Press)

These words, however, are at odds with the testimony of Wilson-Raybould, who claimed that Butts, along with the prime minister and other senior government officials, were involved in the "consistent and sustained effort" to pressure her to intervene in the SNC-Lavalin case.

Butts will have to answer, or want to clarify, accusations that within those conversations there were "express statements regarding the necessity of interfering in the SNC-Lavalin matter, the potential of consequences, and veiled threats" if Wilson-Raybould didn't acquiesce to the prime minister's wishes.

SNC-Lavalin had hoped that its fraud and corruption charges could be resolved with what's known as a deferred prosecution agreement (DPA), which would spare the company a trial and possible criminal conviction. But in October, the Public Prosecution Service of Canada determined SNC-Lavalin had not met the criteria for a DPA.

Wilson-Raybould testified that despite pressure from top government officials, she had made up her mind on SNC-Lavalin and was not going to interfere.

Butts will likely address, or face questions, about at least three meetings Wilson-Raybould raised during her testimony.

'He does not like the law': The ​Château Laurier meeting

Butts will likely give his side of events regarding a meeting he had with Wilson-Raybould on Dec. 5, 2018, at the famous Château Laurier hotel in Ottawa. She had met with Butts, she testified, to speak with him, in part about "the barrage of people hounding me and my staff" over the SNC-Lavalin case.

She said she raised with Butts how she needed everyone to stop talking to her about SNC-Lavalin, that she had made up her mind on the issue and that "the engagements were inappropriate."

But Butts, she said, stressed how they needed a solution on the SNC-Lavalin file and that she "needed to find a solution."

As well, Butts, she said, talked to her about how "the statute was a statute passed by Harper and that he does not like the law. I said something like, 'That is the law that we have.'"

Wilson-Raybould was referring to the Harper government's 2006 Director of Public Prosecutions Act, which, in an effort to quash political interference stated that an attorney general can overrule a decision by the director of public prosecution, but it must be made public.

'Some interference': Meeting with Wilson-Raybould's chief of staff

​Butts is also likely to give testimony about a meeting he, along with Katie Telford, Trudeau's chief of staff, had on Dec. 18 last year with Wilson-Raybould's then-chief of staff Jessica Prince.

At the committee hearing, Wilson-Raybould read from what she said was a text conversation between herself and Prince following the meeting.

Prince, according to Wilson-Raybould, said that Butts and Telford were looking for a solution, wanted external counsel, preferably a former Supreme Court of Canada judge, to give the then-attorney general an opinion on whether she could review her decision.

Jane Philpott, seen here with Wilson-Raybould in 2016, resigned from cabinet on Monday. (Adrian Wyld/Canadian Press)

Wilson-Raybould said that Prince told them that would be interference. Butts is said to have responded: "Jess, there is no solution here that does not involve some interference."

Butts may also be able to comment, or explain, remarks alleged to have been made by Telford, in which she said that if Wilson-Raybould was nervous about revisiting her decision, "we would of course line up all kinds of people to write op-eds saying that what she is doing is proper."

'Are you questioning the integrity of the prime minister?'

Butts may also be asked whether Wilson-Raybould was shuffled out of her role as attorney general because of her intransigence on SNC-Lavalin. Wilson-Raybould said she raised those concerns with both Trudeau and Butts about this issue but they denied that was the case.

In a conversation with Butts, she said she "specifically said that 'I know this has to do with SNC and a decision that I wouldn't take,' to which he said: 'Are you questioning the integrity of the prime minister?' I didn't say anything to that."

How to watch Wednesday's testimony

CBC News will have full coverage of Gerry Butts' testimony at the Justice committee: