Ah, the markets. A bastion of rational thought, predictable trends, and calm, measured responses to global events. Or, at least, that’s what the textbooks tell us. In the era of Donald J. Trump, however, Wall Street often resembles a teenager’s mood swings, lurching from exuberant highs to dramatic lows, often at the whim of a single social media post or a sudden policy pronouncement. The past few weeks have been no exception, offering a masterclass in market volatility driven by presidential pronouncements ...