With two Pulitzer Prizes to her name, Dana Priest is one of the Washington Post’s most celebrated reporters. Until Monday, when the Post published the first installment of a bombshell series on post-9/11 intelligence industrial complex, national security blogger William Arkin was hardly known to the paper’s readers. But from a media perspective, Arkin’s role as co-author of the series might be the more important. It marks the first time one of the Post’s bloggers – lately the cause of controversy because they sometimes blur opinion and reporting — has had a byline in one of the paper’s big, investigative...