When President Donald Trump wanted to make the case for his first term’s success in an interview last month, he turned to the stock market. “I was very proud to have handed over the country when the stock market was higher than it was, previous to the pandemic coming in,” he said in a Fox News interview Feb. 9. “It was an amazing achievement.” And in his second term, he has promised that trend would continue. “The stock market is going to be great,” he told the crowd at an investor conference Feb. 19. But after stocks began a downward...