For months, Goldman Sachs chairman and chief executive Lloyd Blankfein has been the whipping boy for lawmakers and other critics of the securities firm's resilient paychecks, role in the credit crisis and mortgage-related bets.

Now it is Gary Cohn's turn. Goldman's No 2 executive, a longtime confidant of Blankfein, is testifying on Wednesday before the Financial Crisis Inquiry Commission. The congressional panel wants to know more about how derivatives fuelled the crisis, including the near-collapse of insurer American International.