I haven't finished the book yet; but from what I've read, I strongly recommend it. But not without qualification. The book's claims deserve to be scrutinized just as the authors scrutinize "Christian America" claims.
The book's thesis as the authors write on page 17:
We feel that a careful study of the facts of history shows that early America does not deserve to be considered uniquely, distinctly or even predominately Christian, if we mean by the word "Christian" a state of society reflecting the ideals presented in Scripture. There is no lost golden age to which American Christians may return. ...
Their understanding of "Christian" is tightly wound in a theological sense. But the book's chief target is evangelicals who define "Christianity" as something more meaningful than "weak generic" Christendom. As the authors note, "[a]lmost everything in Western culture from the late Roman Empire until about 1800 was 'Christian' in this sense." (p. 30.)
Years ago when I was discussing on my blogs whether the political theology of the American Founding -- although it often presented itself as "rational Christianity" -- deserved the label "Christian," a clever commenter asked whether America was founded on a "Christian heresy."
Although the authors of the book do not believe America's Founding political theology merits the label "Christian," their thesis fits with the "Christian heresy" understanding.
Their thoughts on Winthrop's Massachusetts remind me of the The Simpsons' Founding of the town of Springfield episode that joked the town was founded when "a fiercely determined band of pioneers leaves Maryland after misinterpreting a passage in the bible. Their destination, New Sodom." The Puritians thought Massachusetts was an exalted "New Israel." But the authors claim this a clear case of "mistaken identity" as they put it. (p. 36.) The authors assert Roger Williams' Rhode Island represented the more authentically Christian understanding of government.
But here is where the authors use their authoritative discretion to choose what counts as authentic ideal Christianity, what counts as error. Though, many of the things the authors count as "un-Christian" and consequently put in the "bad" box were arguably part of historic normative Christianity. Religious persecution, chattel slavery, and the deplorable treatment of American Indians are used to solidify the case for an "un-Christian" America. Yet these things were done by Christians in the name of Christianity. Roger Williams who comes out of history smelling better than John Winthrop arguably held more novel and eccentric positions than Winthrop. I'm trying not to "judge," but it seems to me that Winthrop's illiberality was more normatively Christian for the time and context than Williams' liberality that ultimately prevailed in liberal democratic America (and in Western Christendom as a whole).
The authors have been tarred as "liberals" intent on "revising" the record. While I can't say for sure, I don't believe they are either political OR theological liberals. And, in the book, they promote, in addition to Williams, Jonathan Edwards and Samuel Hopkins as model biblical thinkers. They were hardly liberals. And even though Williams' politics were radically liberal for his time, his theology that informed his politics was, ironically, fanatically fundamentalist. Indeed it was America's Founders -- from Washington to Jefferson to Hamilton -- who tended to be theological liberals and consequently not authentically Christian enough. Rather they were the humanists of their day. Albeit theistic/religious humanists.
John Witherspoon was an evangelical Christian. But in his personal theology. When it came to politics -- his Lectures on Moral Philosophy -- he was a naturalist and a (Scottish) Enlightenment rationalist, hardly a "model for Christian political thought." (p. 93.)
On the American Revolution, it violated Romans 13 and otherwise "was not a 'just war' as traditionally defined by the Church, and hence ... was not worthy of unqualified Christian support. ... [Further], the patriots were so hypocritical that they forfeited whatever Christian approval their theoretical justifications might otherwise merit." (p. 95.)
The charged "hypocrisy," you could guess, relates to the patriots' practice of slavery and treatment of the Indians.
I know this is contentious stuff! But it's well worth serious consideration.