There are many damning anecdotes in Kate Conger and Ryan Mac’s new book, “Character Limit: How Elon Musk Destroyed Twitter,” but one from February of last year perfectly captures the astonishing pettiness of the world’s richest man. Attending the Super Bowl as a guest of Rupert Murdoch, Musk had one of the most luxurious seats in the house, but rather than watching the game, he was glued to his phone in dismay. Both he and President Biden had sent tweets cheering on the Philadelphia Eagles, but even though Biden had far fewer followers than Musk on the platform, the president’s...