The Argument: Billionaires, Bloggers, and the Battle to Remake Democratic Politics, by Matt Bai (Penguin Press, 316 pp., $25.95) Matt Bai’s The Argument is the most significant book to date on the upcoming 2008 elections—not because it has anything to say about the horse race for the Democratic nomination, but because it offers an account of the people who constitute what Howard Dean calls “the Democratic Wing of the Democratic Party.” Bai writes regularly on politics for the New York Times Magazine, where some of this material originally appeared. He has been sharply critical of George W. Bush and...