For competent leaders, managing national security and international upheaval involves putting partisan mudslinging on hold. For Prime Minister Justin Trudeau, partisan mudslinging is the whole point. Problems are there to be politicized, not fixed. His latest circus act involved testifying before an inquiry on foreign interference — inspired in part by “irregularities” in a 2019 Liberal nomination race that were uncovered by intelligence officials — to inflame suspicions about the...