In view of the recent push within sociology to promote “public sociology,” it is worth considering the fact that the last two sociological bestsellers have been written by political scientists—both of them, as it happens, at Harvard. First, Samuel Huntington’s 1996 The Clash of Civilizations has dominated post-Cold War thinking about international relations for a generation. Its thesis was first essayed in an article in 1993, at which point it began to influence narrow foreign policy circles. Once it appeared in book form, however, the book’s title (and hence its basic argument) became widely invoked in discussions of foreign policy. Critics dismissed the thesis for its simple-minded reduction of “civilizations” to areas of the world and for ignoring the diversity of viewpoints within those civilizations. But the argument seemed to capture certain crucial truths about the post-Communist world, especially the centrality of “identity” to the ways people thought of themselves when confronted with adversity. In that sense, Huntington stole the thunder of the post-Marxist, cultural-sociological left for an argument that was widely regarded as right-wing. And Huntington drew explicitly on the work of Max Weber in developing his own ideas. Make no mistake: this was a work more of sociology than of what had become an obsessively rationalistic political science, from which it departed in dramatic ways.

The other big sociological bestseller of the past generation was of course Robert Putnam’s Bowling Alone—the argument of which also began life as an article, published in 1995—which decried the decline of “social capital” and its consequences for the country. Because it was focused on domestic affairs, the book was of much greater interest to American sociologists, who tend not to pay much attention to matters beyond their own borders. Like the previous sociological bestseller (this time by card-carrying members of the tribe), Robert Bellah et al.’s Habits of the Heart, the book fit into the long tradition of reflection on the pitfalls of American individualism that goes back at least to Tocqueville. Putnam worried that TV- and electronic gadget-addled Americans have retreated from the voluntary associations that impressed Tocqueville as the true life-blood of American democracy, weakening its civic fiber. Yet Bowling Alone soft-pedaled the rougher edges of American life and the growing dominance in its politics of a profligate financial elite. In this respect, it is noteworthy that, in the preface to a new edition of Habits published in 2007, Bellah mused darkly about the runaway unaccountability of a wealthy “oligarchy” in American life. Nonetheless, Putnam’s ideas caught the attention of the nation and spawned a cottage industry of research on social capital—that is, more or less, on the role of trust, networks, and volunteerism in social life.

Robert Putnam and David E. Campbell’s American Grace follows up on these Tocquevillean themes, exploring the contemporary American religious landscape to understand, in the words of the subtitle, “how religion divides and unites us.” As in Putnam’s earlier work, the book mobilizes the full array of methods available to the social scientist—survey research, interviews, participant observation in relevant settings, historical comparisons. Vignettes drawn from qualitative research are interspersed with discussions of the quantitative data accessible to the uninitiated. The authors draw frequently on other pertinent studies to buttress their own findings, helping reassure us that the results of their research are reliable.

And what are those results? One main finding is that, as compared to thirty years ago (their baseline of comparison), religion and politics have tended to line up more consistently than they had previously, such that people who are more religious tend to be more conservative politically, whereas people who are less religious tend to be more liberal. One of the chief reasons is that younger people have been put off by the association of religion with conservative politics since the time of the Moral Majority. This was itself, according to Putnam and Campbell, a response to the upheavals of the 1960s, and especially to its challenges to gender and sexual norms. Religious-political polarization has been the consequence.

This partisan realignment represents an important shift from a time when churchgoers were more evenly divided between the conservative and the liberal. In those days, for example, many opponents of abortion were liberal on other measures; the reason is that they were devout Catholics who objected to the taking of unborn life but also supported measures to soften the blows of a capitalist economy, which was much less true of their white Protestant political allies. Now, opponents of abortion tend to be the more devout of all denominations (other than Jews), and those more devout people also tend to be more conservative across the board. The association of religiosity with conservatism has driven younger people out of religion, leading to a spike—into the 15-percent range—of the “religious nones,” those who claim no religious affiliation. Needless to say, these trends strongly parallel the contemporaneous emptying of moderates from the Republican Party and its transformation into a strongly ideological grouping lately driven by the sensibilities of the Tea Party.

Still, there remain important exceptions from the tendency for the more devout to be politically conservative. Black Protestants and Jews remain politically more liberal than white evangelical Protestants, while their religion is also much more deeply bound up with their ethnicity than is the case for other Protestants and Catholics. Yet their numbers are rather small. The authors also find that the white evangelical surge actually came to an end in the early 1990s; we have been shadowboxing with it for the last two decades.

Meanwhile, in contrast to a waning mainline Protestantism (there is currently not a single Protestant on the Supreme Court!), Roman Catholicism remains vibrant in the country, but that is mainly because of the large-scale immigration of Latinos since the mid-1960s. The social cohesion of the WASP elite has declined in favor of a more religiously mixed top tier, and the general connection between ethnicity and religion has declined, with the exceptions noted. On the whole, in other words, religion is less strongly associated with other divisions in American social life, which tends to moderate the conflict deriving from the conservative political impulses of white evangelical Protestants.

Accordingly, despite the tendency toward polarization between religious conservatives and less religious liberals, Americans demonstrate a great deal of religious tolerance. Using an example reminiscent of the famously self-worshiping “Sheila” in Habits of the Heart, Putnam and Campbell adduce every family’s “Aunt Susan” as the person who doesn’t fit the family religious tradition but sanctifies her particular faith for them by being such a good person anyway. She personifies the “religious bridging” that they regard as typical of the American experience and the key to its high levels of religious tolerance. Indeed, while acknowledging the country’s sometimes deadly anti-Catholicism in the mid-nineteenth century, the book concludes by gushing that “America has had religious toleration encoded in its national DNA.”

One might wonder here about the relative exclusion from the discussion of the newer religions on the American scene, namely Hinduism, Buddhism, and above all Islam. The stated reason for excluding these groups from the analysis is that their numbers remain so small that reliable statistical analysis is impossible. Fair enough. But the focus on the American mainstream is likely to encounter the same response from critics as it did when Bellah et al. wrote Habits of the Heart—that the book concentrates too much attention on the mainstream and obscures the margins. In view of the extensive mistreatment and opprobrium directed at Muslims in the post-9/11 period, one might ask, can the Putnam/Campbell approach be justified? One answer is that, in contrast to the European situation and to that surrounding such anomalous episodes as the so-called Ground Zero mosque, Putnam and Campbell’s marginalization of the Islam question gives it just the right amount of attention—namely, very little. Islamic extremism engages a vanishingly small proportion of Muslims, but overwhelms all other discussion of Islam (and, of course, drowns out other things that one might pay attention to, such as the approximately five million deaths in the god-forsaken Congo during roughly the same time period as the “war on terror”).

On the other hand, to await the day when newer religious groups achieve a statistical critical mass might keep us from saying anything about them for a long time to come. And whether they like it or not, Muslims in the United States are the subject of a great deal of attention at present and are adherents of the only faith associated with extensive anti-American violence. As even so liberal a publication as the New York Review of Books has pointed out, there is also an increasingly homegrown dimension to anti-American Islamic attacks. Does the religious tolerance in Americans’ national DNA extend to Muslims? Given radical Islam’s targeting of the United States, chiefly if by no means exclusively, should Americans be tolerant of Muslims’ demands for accommodation of their faith when those demands seem at odds with liberal norms? Germany sought to be tolerant but eventually felt that it had to deport the so-called “caliph of Cologne” for his repeated and outspoken denunciations of the German political order. Putnam and Campbell say that the more Americans get to know people of other religions (or of no religion), the more they like them. But what of those—not always Muslims, to be sure—who denounce America as the Great Satan on religious grounds? Liberal societies reach the limits of tolerance when they have to deal with persons who reject the constitutional basis of those societies. This book cannot help us with that debate.

Notwithstanding this quibble, Putnam and Campbell have produced a thoroughly researched, clearly written study of the state of American religion that reminds Americans of what we hold in common and offers the prospect that the polarization produced by the 1960s and its sequelae may be behind us. They do so on the basis of meticulous research using a broad variety of social scientific methods. The book comprises another valuable contribution to sociological efforts to make sense of American life—even if its principal author is not formally a member of the guild. Many sociologists will follow in his footsteps, as will many nonspecialist readers, because American Grace is an outstanding example of public sociology.