Mike Duffy's trial on fraud, breach of trust and bribery charges has brought the national spotlight back onto the suspended senator — and on the Conservative government that appointed him.

The last time Duffy had such a platform — speaking in his own defence before the Senate voted to suspend him in October 2013 — he accused the Prime Minister's Office of orchestrating a "monstrous fraud."

Conservatives took a significant hit in popularity after he revealed that he received two cheques: one from Nigel Wright to cover the Senate expenses he did not want to pay back, and another from the Conservative Party to pay legal expenses.

The party's momentum was brought to a halt and party support slid to a historic low. If the trial that began Tuesday inflicts another blow like that, the Conservative hopes for re-election in the fall would be scuttled.

As for Justin Trudeau's Liberals, judging by the gains they made when Duffy made headlines in the past, they would stand to benefit most.

But has the scandal surrounding Duffy, his living expenses and the $90,000 payment to cover them from Stephen Harper's former chief of staff, Nigel Wright, run its course?

The speeches made by Duffy in the Senate on Oct. 22 and 28, 2013 were only the most explosive moments in a saga that began in May of that year, when the story first broke about Wright's involvement in the repaying of Duffy's inappropriately expensed living costs.

The Conservatives were bleeding support at the time. Trudeau had just been named the new leader of the Liberals and his party was topping the polls.

The extent to which the Duffy scandal had an impact on Conservative numbers, rather than that of Trudeau's honeymoon, is hard to know for sure.

But in the two months prior to the Duffy-Wright story breaking on May 14, 2013, the Tories were averaging 30.2 per cent support in the polls. In the two months after, the party dropped to an average of 28.5 per cent support.

Five of six pollsters in the field before and after Wright's payment made the headlines showed a drop in Conservative support, ranging from two to six points. This rules out methodology as a cause of the drop.

By the end of the summer, the Conservatives were recovering lost ground. The scandal had dropped off the radar and Trudeau's honeymoon was fading.

The Liberals averaged 32 per cent support in polls conducted in September 2013, compared to 30 per cent for the Conservatives. In May, the gap between the two parties had been 11 points.

A historic low

But then came Duffy's speeches at the end of October and their impact was nearly catastrophic for the Conservatives.

From an average of 29.9 per cent support in the two months prior to his allegations in the Senate, the Conservatives dropped to 27.8 per cent. Again, nearly all of the pollsters in the field before and after the event showed a drop in Conservative support.

This pushed the party to a historic low. For the first time since coming to power in January 2006, the Conservatives were now routinely polling under 30 per cent support.

Between the end of October 2013 and early April 2014, spanning 19 consecutive national polls, not a single survey put the party at 30 per cent or higher. Only in the spring of 2014 did the Conservatives finally see their numbers begin to improve.

It was the Liberal Party that benefited from the Tories' discomfort. The party picked up two points in the wake of the story initially breaking, and gained another point when Duffy's Senate speeches gave it new life in the fall of 2013.

The New Democrats made no headway as a result of the scandal in either instance, despite being the only party pushing for the abolition of the Senate altogether.

Duffy fatigue?

If there is some hope for the Conservatives, it is the possibility that Canadians have had their fill of Duffy. Voting intentions may already have the Duffy factor baked in.

While the Conservatives did take a minor hit when the drama made the news again in July 2014, when Duffy was charged with 31 counts including fraud, breach of trust, and bribery, it had little impact on Conservative momentum.

The party was polling at 30.8 per cent in the two months prior to the charges being laid, and was at 30.1 per cent in the two months after. Again, however, it was the Liberal Party that took advantage — temporarily.

Prime Minister Harper must surely be hoping that the Duffy trial will not rock his party like it did in 2013. The hit had been so damaging that observers wondered at the time whether Harper would survive it at all.

But with Wright escaping charges, and issues surrounding terrorism at home and abroad moving into the foreground, the Conservatives have recovered and are running virtually neck and neck with the Liberals. If an election were held today, the party would have better than even odds at winning the most seats.

The Conservatives have been trending upwards since hitting rock bottom in the autumn of 2013, but it has been a long, slow climb back into contention. Being knocked back again, with six months to go before the next election, could be disastrous. Unlike 2013, time is no longer a luxury on the government benches.

This article reviews trends in national public opinion surveys. Methodology, sample size and margin of error if one can be stated vary from survey to survey and have not been individually verified by the CBC.