It is still possible for a Western democratic leader to be held accountable for lying too much. That is the implication of Boris Johnson’s resignation as prime minister of Britain on Thursday, and it’s a hopeful one. Mr. Johnson, elected in a 2019 landslide, once seemed headed for a long career in Britain’s highest office. Yet he could not quite control a habit for shading the truth he first notoriously exhibited in the early 1990s as a Brussels-based journalist writing inaccurate European Union-bashing articles. Mr. Johnson survived a scandal over boozy parties at his official 10 Downing Street residence during Britain’s covid-19 lockdowns. This week, however, he could not withstand a wave of resignations by senior members of his Conservative party government. They were angered at revelations he had falsely denied knowing about sexual misconduct allegations against someone he appointed to a top position.