By David Ljunggren
OTTAWA (Reuters) - Canada's ruling Conservative party is trailing the two main opposition parties for the first time, according to a poll, as a high-profile bribery and fraud trial involving a former Senate ally to the Prime Minister overshadowed election campaigning.
Stephen Harper has struggled to distance himself from the months-long criminal trial of Conservative Senator Mike Duffy, who was appointed by Harper and was once a key party fundraiser, as former key aide Nigel Wright testified for a fourth day.
Harper fired Wright at the height of the 2013 scandal after it was discovered that he secretly gave Duffy a C$90,000 (44,121 pounds) check to cover improper expense claims. He has denied knowing his closest staffer was paying Duffy to make the problem go away.
But four days of testimony by Wright, which continued on Monday, raised questions about how many people in his office knew about the payoff, and how it was possible the prime minister did not.
A Leger poll released over the weekend put the Conservatives in third place for the first time since the campaign started in early August.
Leger said the New Democrats had 33 percent public support, up one percentage point from a month earlier. It cited the economy among one of the main concerns.
The centrist Liberals climbed three points to 28 percent while the right-leaning Conservatives sank five points to 27 percent.
Harper came to power almost a decade ago vowing to clean up federal politics.
Seeking a fourth consecutive term, he faced a barrage of questions about the case at several campaign stops on Monday, while his pledge to increase the number of military reserves to 30,000 from 24,000 drew little attention.
"My responsibility is to ensure that those responsible be held accountable for their acts, and these people are Mr. Duffy ... and Mr. Wright," Harper said at a campaign stop.
An editorial cartoon in the Globe and Mail, Canada's national newspaper, showed Harper's campaign plane struggling to get off the ground, shackled to a ball and chain labelled "Duffy trial", while headlines featured political opponents calling for more Harper staffers to be fired.
"Mr. Harper has not been truthful with Canadians - that has become abundantly clear from the emails that have been released, and Canadians deserve better," said opposition leader Thomas Mulcair, whose left-leaning New Democrats are leading Harper's Conservatives in opinion polls.