Jimmy Carter may be the most pious man ever to have occupied the White House. He was “born again” at age 11 and has taught Sunday school for decades. His penchant for godliness has ranged from prophetic — he was most likely the only businessman in 1950s Plains, Ga., to refuse to join the White Citizens’ Council — to priggish: As president, he once told civil servants who were “living in sin” that they ought to get married...

Balmer presents Carter as an icon of progressive evangelicalism, a subculture that was coming into its own in the 1970s as young Christians like Jim Wallis rallied believers for civil rights and against the Vietnam War. These evangelicals traced the roots of their crusade to the abolitionists and other 19th-century moral reformers.