Shoppers in a Target store in New York City. The number of shoppers visiting Target stores has fallen since the retailer triggered a customer boycott by indicating it was pulling back from diversity initiatives it had long promoted. Photograph: Michael M Santiago/Getty Images Bit by bit, one by one, they started to come out. After days of market mayhem, America’s billionaires finally did something this week that few top bosses have done since Donald Trump took office in January: sound off about the US president’s actions. Trump’s sweeping tariffs, they said, were a “huge policy mistake” born of “stupidity” that...