After failing to criminally prosecute any of the financial firms responsible for the market collapse in 2008, former Attorney General Eric Holder is returning to Covington & Burling, a corporate law firm known for serving Wall Street clients. The move completes one of the more troubling trips through the revolving door for a cabinet secretary. Holder worked at Covington from 2001 right up to being sworn in as attorney general in Feburary 2009. And Covington literally kept an office empty for him, awaiting his return. The Covington & Burling client list has included four of the largest banks, including Bank...