Billionaire investors are in an unfamiliar position, watching and cringing as tariffs roll on and the stock market reels.Wall Street billionaires are not used to being on the outside looking in. But that is where they find themselves after President Trump ignored their appeals to call off his tariff plans which they fear could endanger the economy. With the backdrop of rapidly mounting stock market losses, corporate titans have worked every angle — phone calls, social media and even a typically staid shareholder letter — to try to change Mr. Trump’s mind. The day after the president announced his most...