Vladimir Putin’s nuclear threats have been menacing and apocalyptic. In March 2018, he told an interviewer that he would not start a nuclear war, but if “aggressors” attacked Russia, “vengeance is inevitable.... We will go to heaven as martyrs. This is not a bluff.” And then he led the crowd in chanting, “Russia, Russia, Russia.”President Joe Biden suggested last week that the “prospect of Armageddon” hasn’t loomed so close in 60 years. Are Mr. Putin’s threats serious or mere saber rattling? Are they calculated bluffs to frighten NATO and deter intervention, or bellicose rants from an isolated and unhinged bully?

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