Because this certainly wasn't what he was saying, but I do think that despite the best efforts of the Founders (capitalized?) who were most certainly not Xtian in any conventional sense, we have certainly become a Xtian nation, in the sense of the relationship between religion and the state. Again, this isn't what McCain was saying, but just something to consider. The cruel irony is, of course, how so many of the Founders were deists or had little interest in religion in an organized sense. And yet, the idea that we were founded as a Xtian nation has some of the most permanence of all of our beloved myths.

That said, wearing a kippah in the midwest really makes one realize how Xtian this nation is.

The founders, if we read the Constitution and other founding documents (and arguments that led up to those documents, like the Federalist Papers), carefully set up a system of government unfettered by religion, but infused with their own religious principles.  This makes us, in terms of law, decidedly not a Christian nation--not a theocracy, not in the business of requiring Christianness as a part of Americannness.  That said, in practice we have been a Christian nation, measuring all faiths by the yardstick of Protestant Christianity.  I have suggested this book on other posts, but it bears repeating: Janet Jakobsen and Ann Pellegrini, Love the Sin: Sexual Regulation and the Limits of Religious Tolerance. 

Knotty theodicy confronts nitwits like McCain and patriotic fundamentalists here, apart from their self-congratulatory air because they purport to be Christians. (Me, I always thought they were Protestants, and God was cursing them endlessly with besetting, fruitless, myopic, fissile quarrels among themselves):

Why did God wait 1776 years after the putative birth of Christ to set about establishing said Christian nation? If this was the way to go, 33 CE would have been nicer--given Bar Kochba and the Zealots a better deal too. Not to mention 1915 years of trouble for the Jews.

Why did God pick a continent whose very existence was not suspected, in a hemisphere that was "recognized" to have no landmass, in a language not even a faint inkling of which was discernible in 33 CE, and a secular constitutional regime that gave human slavery and genocidal policies toward the native inhabitants a legal basis, to declare His National Purpose? Must pursue sometime the lack of even a hint in any Scripture that this US Project was to come. That absence of any explicitly declared Divine Sanction is what caused major anxiety among Protestants though, with all their Scriptural fictions. So they wrote some new ones, and they are still writing them . . . ).

Why did God pick a bunch of lawyers to carry off the covert Christianization of the state. Why were policies so ineffective that the country fell into a bloody civil war a mere 85 years later. Why are we still litigating effects of that war?

The only possible resolution is that the United States is the Second Coming of Christ. And that is all that Murricans like McCain get by way of salvation. God plays gotcha! every day with the arrogant.

I think Adam is right - the myth of the US being founded as a Christian nation stems from its evolution into one... The Enlightenment (and secularism generally) influenced the founding generation profoundly, and with it the constitutional structures of the United States. But almost immediately thereafter disasters such as the second "Great Awakening" and the Holiness movements Christianized American society to a great extent.  America's Christian tendencies have come and gone in waves, with the first of these striking in the early nineteenth century, and the second around WWI and the publication of the Fundamentals.  While late Eighteenth century American may not (and there is evidence on both sides of this argument) have been a Christian nation, and 1920s American had quite a few prominent (and beloved) atheists in public life, the overall trend has been a Christianizing one.  And since Jimmy Carter's administration, let's face it, the public image of American government (or at least it's executive branch) has been largely Christian, with varying shades of emphasis (and varying levels of fanaticism).