Tom Yeung here with your Sunday Digest. In 2008, Citigroup Inc. (C) was in trouble.  The bank had poured billions into mortgage-backed securities, and these complex instruments were now blowing up in their faces. The firm even became the poster child of foolish Wall Street risk-taking after its CEO, Chuck Prince, tried to defend his bank’s actions by quipping, “as long as the music is playing, you’ve got to get up and dance. We’re still dancing.”  The U.S. government knew the bank had danced its way into di ...