The website Patheos asked me to answer the above question, in no more than 800 words. Here's what I came up with (a slightly edited version is here, as part of a re-launch of their "Public Square" feature):
Robert Bellah's classic notion of America's civil religion involved, as he put it, "the subordination of the nation to ethical principles that transcend it." To elaborate on that idea somewhat, Bellah held that the United States of America--like, he believed, every sovereign national body--both carried within and articulated through its own history a "religious self-understanding": in our case, a Judeo-Christian one, in which the ethical principles of the Ten Commandments and the Sermon on the Mount formed a commonly accepted baseline upon which American citizens assessed their own polity (and, in particular, its political leaders and government policies). Bellah himself later backed away from a strong reliance upon civil religion as a way of explaining American society or diagnosing its behavior, emphasizing that the American religious ideal is best conceived as an wholly internalized, non-institutionalized one, but his original formulation still haunts many American political debates. In a country with a strong Protestant Christian history, comparatively robust levels of religious affiliation, ever-increasing religious pluralism, and numerous politically active religious-oriented groups and a party factions, what role should, or can, civil religion play?
My attitude towards these questions is fairly straightforward: I think that asking whether civil religion is possible or needful ignores the reality that it is, in fact, inevitable in a free and democratic society. Developing in the elaboration of some kind of civil religious consensus is a by product of thinking and believing people freely interacting with each other. In fact, I do not think that the "religious self-understanding" which Bellah observed about American life is necessarily all that substantively different from one of the great bogeymen of American constitutional history: "religious establishment." Bellah's later effort to insist that a civil religion loses its coherence when conceived outside of the individual dimension is, I think, a retreat from what is an otherwise inescapable complication.
In my view, it is an unavoidable facet of human nature to want to understand the actions of individuals (including oneself) as embedded in some sort of collective, morally (and often religiously) substantive--that is, “truthful”--cultural order. This is the fundamentally communitarian and dialogic character as human beings coming out: our ability to speak, think, associate, and judge impels us to retrieve from or construct through our social lives an arrangement of meaning. The result of this will be, in all but the most demographically unsettled and historically conflicted polities, a broadly affirmed civil religion which will invariably push towards elaboration and codification, even if at the same time one might be reluctant to grant the legal extremities of such, and even if the venues for expressing that codification (government offices, public schools, sporting events, marriage rules, family policies, etc.) vary and grow more diverse over time. America is not an exception to this; religious historians and political theorists (Jan Shipps and Eldon Eisenach, to just name two) have long argued that America's civic identity has been shaped by a series of what might be called "voluntary national religious establishments"--and there is no reason, I think, to believe that process has ended. Indeed, if that process came to an end, it would imply rather threatening conclusions about the reality of our own freedom as thinking, believing, associating beings and citizens.
America's civil religion today has a very minimal establishment, which mostly finds its expression in genially liberal ways. But that does not mean it is absent. The depth of the animosity which long characterized the debate over same-sex marriage--and the near-panic over protecting "religious liberty" which now characterizes the way some culturally conservative Christian churches and organizations are viewing same-sex marriage's recent successes--should make that clear. All the participants in this debate would do better, I think, if they could appreciate the substance of the ground upon which they are arguing. On the secular side of this divide, there is the insistence that they merely seek government neutrality, and have no theological agenda. This, I think, is clearly false; a society which carries into wedding halls, however implicitly, civil religious assumptions which can accommodate the idea of same-sex unions is going to be a very different society from one which rejected that idea as perverse. On the other, conservative side, there is the insistence that defensive actions against proposed rules about marriage or contraception which they make on behalf of religious traditionalism is a matter of preventing the public square from being stripped naked of all religiosity. But of course, it isn't that at all: rather, it is clearly a matter of particular Christian communities--ones which have long enjoyed implicit advantages under our reigning civil religion--losing their default position.
The partisans of those communities--those particular religious believers, in other words--obviously use whatever democratic or constitutional tools are available to them to protect their established presumptions. And sometimes, particularly in certain parts of the country, such legal and majoritarian strategies will work, and the resulting establishment will be a hybrid, contentious one. Wishing to avoid such contention entirely is, I think, a false and misguided hope. Democratic societies will have common religious understandings of one sort or another. The fact that America's is currently turning from a liberal-but-nominally-orthodox Christian one into something else is a legitimate concern for conservative believers--but it does not mean that civil religion will disappear, or that anyone should want it to.