American political discourse regularly features the assertion that the United States was founded as a Christian Nation. The debate around this issue often pivots on the religious proclivities of the founders themselves. According to the logic of framing the matter in this way, proving that the founders were themselves Christians clinches the point in favor of Christian nationhood. Alternately, emphasizing that certain founders lacked zeal, embraced deism, or rejected basic tenets of traditional Christianity, such as the divinity of Jesus, is taken to prove that they did not intend to create a Christian Nation. This debate, like so much else about religion in the public sphere in the United States, has been badly framed.
The separation of church and state at the federal level aimed at reassuring people that no version of religion would be promoted by the state. These assurances appeared necessary. Americans wanted to avoid the problems plaguing Europe. Most Europeans lived under legal systems that established one version of Christianity and persecuted those who did not adhere to the state church. In some places that persecution was mild -- blocking the wrong kind of Christians from holding public office or attending university, for instance; in other cases it was brutal -- exiling all Protestants from France or warring against those of other faiths (in the "Wars of Religion" initially). These well-known religious politics made many Americans decidedly nervous that one religious group gaining the upper hand might impose limitations upon or even commit violence against those of other groups. A strong central government, as the Constitution aimed to create, would be able to adopt coercive policies, and those who hesitated to endorse its creation feared above all else that such power might be turned against their own freedom to believe or practice as they wished. Hence this assurance was enshrined in the first amendment to the Constitution, promised along with other amendments in advance of the Constitution's adoption to assuage these worries.
True religious freedom, of the sort the United States eventually came to adopt, was also part of the revolutionary conversation. Captured most clearly in the Virginia Act for establishing Religious Freedom, this position promised everyone that regardless of their faith (or lack thereof), the government would not concern itself with matters of conscience. This agreement arose out of a compromise across a wide range of viewpoints. The unconventional Thomas Jefferson, raised an Anglican (in our parlance Episcopalian), rejected traditional Christianity in adulthood. While he wanted freedom from coercion to believe anything in particular, his strongest allies in the fight were Baptists, who wanted the same, but from the very different position of deeply faithful people who wanted to be left alone to believe and worship as they liked. They knew that the individual states much less the nation would never endorse a religious establishment that upheld their Baptist faith, so part of their support came out of fear of the tyranny of other Christianities. Yet, even if they had thought the government could be gotten to coerce conformity to their particular views, they remained opposed to a religious establishment or any government involvement in religion on principled grounds. They argued that the nation and Christianity should hold each other at arm's length. In other words the believers most similar in their faith to the advocates for Christian nationhood today explicitly opposed the creation of a Christian nation. They believed such a construction would ultimately be bad for Christianity.
Clearly the idea that Christian founders thought, as do one subset of contemporary American Christians, that the United States ought to be a Christian Nation is false. The decision to separate religion and politics, to create a secular nation that made belief a private matter, earned wide endorsement. The question was not whether they were themselves deeply Christian (some were, others not). Rather the point at issue was how to keep religion and politics separate, for the safety and health of both.