Two of the three, Mike Duffy and Pamela Wallin, were well-known broadcast journalists who, after joining the Senate, often used their celebrity to draw crowds at Conservative fund-raisers throughout the country.

At the heart of the controversy are rules that allow senators who live more than 100 kilometers, about 62 miles, from the capital to claim living expenses when here.

Mr. Duffy was appointed as a senator for Prince Edward Island, his birthplace, although has lived far to the west in Ottawa for most of his adult life. It was not until after his appointment that he declared his summer cottage on the island his permanent residence for Senate purposes. But a Senate inquiry found that when it came to everything else, including as his government health insurance and driver’s license, Mr. Duffy claimed residency in suburban Ottawa.

The Conservatives first tried to quell the controversy by announcing that Mr. Duffy had voluntarily repaid $90,000 for expenses collected over four years. But that gesture only made matters worse when CTV — coincidentally the network for which Mr. Duffy and Ms. Wallin had worked — reported that Mr. Harper’s chief of staff, Nigel Wright, had given Mr. Duffy a personal check to cover the $90,000 reimbursement. Mr. Wright resigned from Mr. Harper’s staff soon after news of the check became public.

The prime minister, who has a reputation as a micromanager, has denied knowing anything about Mr. Wright’s check before it became public and has offered no explanation for Mr. Wright’s generosity.

Mac Harb, the sole Liberal among the four senators, had been in the House of Commons, representing the downtown Ottawa electoral district that includes the Senate chamber, before he was appointed to the Senate. But court statements filed by the Royal Canadian Mounted Police to obtain a search warrant indicate that once a Senate appointee, Mr. Harb changed his declared residence to a house just outside the 100-kilometer limit, allowing him to claim expenses. However, that dwelling, the police said, was uninhabitable for an extended period. Mr. Harb recently repaid $232,649.07 in expenses and resigned; he now collects a parliamentary pension of more than $100,000 a year for his service in both houses.

The Conservative motion to suspend Mr. Duffy, Ms. Wallin and a third senator, Patrick Brazeau, who is also accused of lying about the location of his primary residence to collect expenses, seems to have only added to public skepticism about Mr. Harper’s role and his knowledge.