Bob Ortega is an investigative journalist for The Wall Street Journal. He's the author of the new book, "In Sam We Trust: The Untold Story of Sam Walton and How Wal-Mart Is Devouring America" (Times Business/Random House). The book looks at how Wal-Mart went from a tiny variety store in backwater Arkansas to one of the world's largest corporations. In doing so, Wal-Mart's business practices have been imitated by other businesses and criticized for its impact on communities, and treatment of workers.