GARY COHN, the current head of the National Economic Council, likes to say he is a fan of bad decisions. “I’m really good at making mistakes,” he told business-school students at Sacred Heart University last year. And at American University, his alma mater, in 2009: “I always saw 95 percent of my great decisions start out as bad decisions.”
Last November, when Cohn walked into Trump Tower, he didn’t expect to be making decisions of any kind. He was there, like Floyd Mayweather before and Kanye West after him, because he had been summoned. In his case, to impart the macroeconomic wisdom he possessed as president of Goldman Sachs onto the newly elected president of the United States: Donald Trump, the man the smart money said would never win.
“It…