This is really beginning to bother me. America has never been a Christian nation, and never will be. Such an idea is a logical impossibility, if Scripture such as Matthew 7:13 means anything at all. That verse states (NASB), "Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it." Furthermore, history itself invalidates this conception. In addition to the article linked above, there are other good articles on this as well.
FFRF: Is America a Christian Nation? No.
AU: Is America a 'Christian Nation'? No.
Biblical Discernment Ministries: Is America a "Christian" Nation? No.
Atheism.About.Com: America a Christian Nation? No.
Skeptic Tank: Is America a Christian Nation? No.
And in the interest of fairness, I will post an article which is not as supportive of my views as I would like.
Catholic Education: Is America a Christian Nation? Yes and no.
Please understand, I am a Christian. I do not endorse any of the above sites necessarily, except wherein I find agreement with their views. Explicitly, for the purposes of this blog post, that means I endorse the view that the belief of America being a Christian nation is a myth. As serious Christians, we really ought to practice our holy faith and devotion in reality as we find it, not as we would like it to be (and I sincerely desire that this myth were completely truthful instead!). I for one believe that the Scriptures which speak of being "Salt and Light" in Matthew 5:13-16 are much more important than earthly political identifications and partisan struggles anyway. Or at least, they SHOULD be.