There seems to be little doubt that President Obama will nominate former Justice Department official James Comey to lead the F.B.I. There has been no official announcement from the White House about Comey's nomination, but NPR broke the news after talking with sources who apparently have knowledge of the search to replace the current director, Robert Mueller. Comey, a Republican, was deputy Attorney General during the former Bush administration, and he also served as federal prosecutor for the Southern District of New York.   Ronald Kessler,  author of The New York Times bestseller, "The Secrets of the F.B.I.," explains what this nomination means.