Most economists—including Krugman himself—have regarded the late 20th century divergence as resulting largely from changes in technology and trade, but now Krugman writes—particularly in Chapters 1, 3, and 4—that government policies—particularly the establishment of, and subsequent attacks on, the social safety net or "welfare state"—has played a much greater role both in reducing the gap in the 1930s through 1970s, and in widening it in the 1980s through the present.

Nevertheless, Krugman expresses optimism in Chapter 10 that demographic trends—particularly on race and culture—and what he sees as conservative overreach during the Bush years—are creating a new center-left political environment and are slowly undermining the conservative movement, referencing John Judis and Ruy Texeira's book, The Emerging Democratic Majority.

The book concludes with advice that, for the time being, liberals must be partisans until both major political parties accept the rationality of the New Deal.

[6] In a review for The New York Times, Pulitzer Prize-winning historian David M. Kennedy stated: "Krugman's chapter on the imperative need for health care reform is the best in this book, a rueful reminder of the kind of skilled and accessible economic analysis of which he is capable, and how little of it is on display here.

Like the rants of Rush Limbaugh or the films of Michael Moore, Krugman's shrill polemic may hearten the faithful, but it will do little to persuade the unconvinced or to advance the national discussion of the important issues it addresses.