The Covenanters, now mostly forgotten, were America's first Christian nationalists. For two centuries they decried the fact that, in their view, the United States was not a Christian nation because slavery was in the Constitution but Jesus was not. Having once ruled Scotland as a part of a Presbyterian coalition, they longed to convert America to a holy Calvinist vision in which church and state united to form a godly body politic. Their unique story has largely been submerged beneath the histories of the events in which they participated and the famous figures with whom they interacted,...