In a down year for stocks, the 70% drop in Tesla’s share price stands out for the scale of wealth vaporized and the unorthodox behavior of its CEO, Elon Musk. The collapse of Tesla’s stock price destroyed about $680 billion in market value. And Musk, once hailed as a genius who remade the car industry, appears increasingly distracted by his acquisition of Twitter and is using the social network to vent his frustrations. He insulted one of his critics this week by describing him as having “tiny testicles.” The spectacle has stunned investors and analysts. And many are asking what...