OTTAWA (Reuters) - A former ally of Canadian Prime Minister Stephen Harper goes on trial for fraud and bribery on Tuesday in a case that could damage the governing Conservatives’ chances of winning October’s general election.

Now suspended senator Duffy arrives on Parliament Hill in Ottawa in this file photo from October 22, 2013. REUTERS/Chris Wattie/Files

Mike Duffy, a former television reporter who became a popular fund-raiser for the Conservatives, faces 31 criminal charges related to activities after Harper appointed him to the Senate, the upper chamber of Parliament.

The trial could present an acute challenge for the right-leaning Conservatives, who came to power in early 2006 promising more government accountability.

The party that talked about cleaning up politics looked less than transparent when it emerged in May 2013 that Harper chief of staff Nigel Wright had given Duffy a C$90,000 ($72,000) check to cover living expenses the senator had claimed improperly.

Wright quickly quit. Harper insisted he knew nothing about the check, even though police uncovered an email from Wright saying Harper had discussed the Duffy case with him.

Harper later said he had, in fact, fired Wright. Opposition members of Parliament questioned how a man known for imposing tight control over government knew nothing about the scandal.

A string of senior Harper officials will appear during the trial and opposition parties are watching closely.

“What was the prime minister thinking to allow this culture of corruption and breach of trust to happen right around him?” legislator Charlie Angus of the New Democrats said last week.

Duffy and two other senators have been suspended from the chamber due to charges they filed improper claims for living expenses. All three were appointed by Harper.

“They’re like iron chains dragging at his feet,” Angus said.

The case comes as a number of Conservatives leave government. Foreign Minister John Baird quit abruptly in March, and last Friday two other cabinet ministers announced they would not run in October.

Polls show the Conservatives are tied with the opposition Liberals and will have trouble retaining their parliamentary majority in the election.

Duffy denies the charges against him and promises sensational revelations. Privately, Conservatives say the trial will be embarrassing, but they doubt Duffy has more bombshells.

The party has long since disowned him.

“He is accused of taking illegal expenses and if he is found guilty of that he should face the full extent of the law,” said Paul Calandra, Harper’s parliamentary secretary.

The trial is scheduled for 41 days in April, May and June.

($1=$1.24 Canadian)