Marco Rubio argued that Western counterterrorism has had a longstanding “blind spot” toward left-wing violence. During a speech before 66 countries on Thursday, the Department of State head described a new transnational wave comparable in character — though not yet scale — to the revolutionary terrorism of the 1970s. “Between 1970 and 1980, 93% of terrorist attacks in the West came from the far extremist left,” he said. “These are numbers that would shock most Americans today because we’ve been taught to believe that this kind of political violence, it simply doesn’t exist, or it’s being exaggerated. But it does...