Yeah, I agree; I wrote that comment very quickly and needed something better than "whatever you want to call the expertise required to understand the issues involved in Watergate and in reporting Watergate". I brought it up because I think it's pretty funny to have a "no journalists, except when they're writing about journalism" rule. Nobody was interested in _All The President's Men_ because they wanted a Jack-Shafer-esque inquiry into the media and the practice of reporting; what made the book influential is the reporting Woodward and Bernstein performed.
If you want a replacement example that isn't make that point, substitute in Lawrence Wright and either scientology or terrorism.
Neither of their books were really about constitutional law. "All the President's Men" is in the "Books about journalism" section of Wikipedia.