The United States is not, nor has it ever been, nor will it ever be, a Christian nation.
Even if the Fundamentalists get their way and manage to not only take over but manage to install a theocratic Christian government, it wouldn't be the United States of America. It would be a zombified imposter pretending at the name.
There is no Christian ideology (or even Biblical ideology) to be found in America's founding ideals. None of it, not the Declaration of Independence, the Constitution of the United States, the subsequent Amendments to the Constitution, the laws that have been generated since then, and our system of government derived therefrom has anything to do with Christianity or the Bible. If anything, the American system is a radical and emphatic rejection of Biblical ideas regarding laws and government.
The Bible, in case you missed it, promotes the so-called "Divine Right of Kings" and theocratic dictatorship. These two ideals are at the core of the Abrahamic governmental tradition, and America just isn't about that sort of thing.
Diametrically opposed to the idea of a God-appointed King and a set of laws that commands you to revere one particular religion (thankfully), the legal system of the United States of America was instead based on English common law, as established primarily by the Magna Carta in 1215, the British Constitution of 1657, the Habeus Corpus Act of 1679, and the English Bill of Rights of 1689.
None of these drew from Biblical government philosophy, either.
Instead, they were based on a pair of pagan legal philosophies: Greek democracy (which promoted the idea that citizens got a say in how the government did things) and Roman civil law (that promoted the idea that the law treated everyone under it in the same non-prejudicial way). Other important inspirations for the American system of government were obtained from philosophers of the Enlightenment Period, principle among them John Locke, Voltaire, Rousseau, and Montesquieu. There is also some evidence that Benjamin Franklin brought ideas from the Iroquois Confederacy's form of democracy into the mix, particularly the idea that each state would be an autonomous unit bound to a larger federal whole.
If the founding fathers had intended the United States to be a Christian nation, you'd think they might have included the words "Jesus," "Christ," "Bible," or "Christian" somewhere in the Declaration or the Constitution. But they didn't. What, do you think they did that accidentally? No, not at all. On the contrary, they intentionally left religion out, and did so for some very, very, very good reasons.
The first reason was that a lot of the founding fathers simply were not Christian. Along with other great thinkers of the Age of Enlightenment, people like Thomas Jefferson, Thomas Paine, John Adams, James Monroe, and many others were rethinking long-held ideas regarding religious doctrine, religious dogma, and religious "tradition" and were finding much of it contrary to their sense of justice, morality, and spirituality. They found that some of the most widely-held religious dogma stood in direct opposition to the ideals of freedom and equality for all. The rise of modern scientific thought had begun to undermine the Bible's simplistic (and utterly incorrect) teachings regarding how the world worked, and as a result these learned men began questioning. If the Bible was wrong about so many things, what else was it wrong about? Thomas Jefferson went so far as to publish his own version of the Bible, one that left out everything he personally disagreed with. It ended up being a comparatively short, rather compact volume.
Many of the founding fathers identified themselves as Deists. Not Christians. Not even theists. But Deists. They still believed in a god, but refused to believe that god would break his own laws of nature to interfere in human affairs.
The second reason was that the founding fathers were very aware of the disasters caused when religion and government mixed, as had occurred in England and throughout the rest of Europe, as well as in the early American colonies where, for example, being a Quaker in Massachusetts was to court being tried for "heresy" and put to death by hanging. The founders had absolutely no intention of adhering to "traditional Christian values" of treating those who you disagreed with in a brutal, bloody, and barbaric manner. They could look at the history of Christian vs. Christian violence that had ravaged Britain and Ireland and Europe during the Thirty Years War, the English Civil War, and the continual "Troubles." Now would they countenance anything like a government-sponsored religious crusade against "infidels" like the heathen Cherokee or the Catholic French.
As such, the founding fathers made the extremely wise choice to wholly and utterly exclude religion from the government. Any religion could flourish freely, and hopefully peacefully, in co-existance with all other religions, but would lack any sort of public support or institution. In the United States, you could be an Anglican or a Quaker or a Catholic or a Muslim or a Hindu or even an Atheist and not be compelled into obedience of anyone else. It was a brand new concept called "freedom of religion,", though it could easily enough also be called "freedom from religion." Any way you want to look at it, this freedom is one of the central pillars of our society and is one of the most important building blocks in our collective awareness of what freedom means.
Not only is the idea that the United States is Christian a false one, the idea that we used to be more religious than we are now is also false. At this time, about 60% of the population of the United States self-identifies as religious (and that's counting all religions). Religious affiliation as a percentage of the population actually peaked in the 1980s. In 1800, that figure was only 9%. During the Civil War, the number of people who identified themselves as religious was only about 20%. And today its nearly 60%. So no, we weren't more religiuous in the past. For the record, the percentage of people who identified as religious has been dropping steadily every year since 1983. People who do not go to church and who identify with no religion at all are the fastest growing segment of the population. The number of non-believers currently stands at 20% of the population. Last year it was 14%. If things keep going the way they're going, next year it might be 35%. Pretty soon we'll be right back at the 9% religious population of the founding fathers.
Obviously, a "Christian America" never existed, nor was it ever intended to be created.
But for the sake of argument, let's play a game of "Let's Pretend."
Let's suspend all common sense and fantasize for a moment that America really was supposed to be a Christian nation. Let's ask ourselves just what exactly that would mean?
What precisely is a "Christian nation?"
What other nations can we hold up as examples of such a government? Byzanium under Constantine? Italy during the Renaissance? Jean d'Arc's France? Henry VIII's England? Martin Luther's Germany? The Denmark portrayed in William Shakespeare's Hamlet?
Which version of Christianity are we going to base our "Christian nation" on? There are hundreds of distinct variations of Christianity, and some of them hate each other with a rage that burns as hot and bright as a supernova. Will our Christian nation be Catholic? Orthodox? Anglican? Evangelical? Episcopalian? Mormon? Pentecostal? Quaker? Or maybe something really obscure like Milleritism or Cooneyitism?
Would our Christian nation be based on the love, forgiveness, and pacifism of Jesus Christ? Or on the bloody violent crusader mentality that came along later?
And who gets to choose all these things? Would we vote on which kind of Christianity we followed every four years, in the same years we voted for a new president? Might we swing from the "love thy neighbor as thyself, feed the poor, turn the other cheek" kindly Christianity to the "kill them all for God will know their own" bloody violent Christianity overnight when the Christian-Republicans win out over the Christian-Democrats? Would we be open and accepting of other religions, or would be lynch the unbeliever and heretic from the nearest lamp-post as a warning to the devil-worshipping heathens that their ways will not be tolerated?
Its all very vague. Just like the real meaning of the phrase "Traditional Christian Values."