G.K. Chesterton once remarked that America was “a nation with the soul of a church.” This remark is frequently held up as an apt description of a country that remains relatively religious even as Europe secularizes, that's still highly moralistic in its understanding of itself and its role in the world, with a history of producing cults and undergoing periodic spiritual awakenings. America does not have an officially established church, so Chesterton’s remark points to something different: an unofficial religion and system of values that pervades the country’s politics and culture and sensibilities, something often referred to as America’s civil, or...