OTTAWA—The Supreme Court of Canada will not hear Sen. Mike Duffy’s challenge of a ruling that prevents him from suing the Senate for suspending him. The decision could be a fatal blow to Duffy’s efforts to wrest $7.8 million in damages from the Senate, RCMP and federal government. Duffy filed a lawsuit following a high-profile investigation of his expense claims, which culminated in the Prince Edward Island senator’s acquittal on 31 criminal charges in 2016. In late 2018, an Ontario court ruled the Senate’s decision to suspend Duffy was protected by parliamentary privilege, a ruling upheld on appeal, effectively blocking his bid to sue. In their submission to the Supreme Court, Duffy’s lawyers said he was the victim of arbitrary abuse of power by public officials, which is anathema to the rule of law. Lawyers for the Senate argued parliamentary privilege plays a vital role in maintaining the separation of powers between the legislative, executive …