In May 2007, when Barack Obama was but an upstart challenger of Hillary Clinton, he attended a gathering of several dozen hedge fund managers hosted by Goldman Sachs at the Museum of Modern Art in New York. It was not a fund-raiser, just a chance for Obama to introduce himself to the investment wizards who had helped turn the hedge fund sector into the most lucrative and alluring corner of the financial universe. And the first question for Obama was as blunt as one would expect from this crowd. “If you’re elected president,” asked one guest, “what will you do to the taxes on the people in this room?” “I’ll raise them,” Obama fired back. “Which I admired,” recalls one of the attendees, Leon Cooperman, head of Omega...