People trying to turn America into a "Christian nation" have systematically distorted and falsified the religious views of the nation's founders. Their critics have sometimes erred in the opposite direction, painting a heavily non-Christian picture of the founders. David Holmes, a professor of religious studies, avoids both errors and gives a convincing account of the dominant view of their religious philosophy in The Faiths of the Founding Fathers.
The eighteenth century in America was influenced by contrary religious trends. On the one hand, the Enlightenment led to deism, a belief in the "God of nature" rather than the "God of Israel." On the other hand, the Great Awakening which began in the 1730's advanced "born-again" Christianity and was, in Holmes' words, "the single most transforming event in the religious history of colonial America."
Deism wasn't a single, monolithic doctrine. Most American Deists still called themselves Christians, though rejecting some Christian doctrines. The more radical ones, such as Thomas Paine and Ethan Allen, were strong opponents of Christianity. Few, if any, believed in a completely non-interventionist God. Deism influenced most of the founders to varying degrees, with Franklin and Jefferson being among the clearest examples.
Holmes discusses Unitarianism alongside Deism. The Unitarianism of the eighteenth century shouldn't be confused with modern Unitarianism; its adherent considered themselves Christians, but rejected the ideas that God was a Trinity or that Jesus was divine. To modern Evangelical Christians, this is heresy, but Holmes notes that the Trinitarian view didn't become the only acceptable Christian doctrine until late in the fourth century. Holmes considers John Adams a Unitarian and a Christian Deist.
Where the evidence isn't clear, Holmes acknowledges the fact. George Washington's religious views have always been a subject of debate, with mythologizers such as Parson Weems (who invented the cherry tree story) adding to the confusion. He notes that Washington was a regular churchgoer but probably avoided the communion sacrament, and that he generally didn't use specifically Christian language, and regards Washington as a "Deistic Episcopalian."
The book notes that some of the founders were Christians in the orthodox sense, and gives some details on Samuel Adams, Elias Boudinot, and John Jay. He also notes that the wives of the founders were Trinitarian Christians much more often than their husbands.
The epilogue contrasts the earliest presidents with the most recent ones. Holmes states that "[s]ince 1976, every presidential election except that of 1988 has had at least once self-avowed evangelical Christian running as a major party nominee." These don't include just Republicans; Jimmy Carter's evangelical Christianity was anything but a secret, and Bill Clinton has publicly called himself a born-again Christian.
For those who want to refute the claims that America's founders were the model for today's religious right, while avoiding secular exaggeration, The Faiths of the Founding Fathers is a worthwhile and readable book.