link). Hence, from a purely theological perspective Christians in USA should very much resemble Christians in Northern Europe. But, they surely do not!
They base their religious beliefs on the same religious scriptures, but still they differ so vastly to the extent that one could easily mistake them for separate religions all together. And why is that? Well, of course because the culture is so very different. It's actually quite understandable. In order for new nations to survive they have to unite the people under one banner. Most of the old European countries have a long history and ancient mythological roots that bind them together. This was no easy task for the founding fathers. USA is a very big and heterogeneous country. Basically they only had two things in common. The fact that most of them had left Europe (often due to religious and political persecution) and were Christians. This is probably one of the big reasons the government was declared secular.
Atheist often like to point out that many of the founding fathers were non-believers or deists. That of course contributed to how the constitution was formed. But, frankly that was also the only way to unite such a heterogeneous group of people of whom many had been persecuted by the governments in their former countries that did not tolerate religious dissidents.
But, most Americans were devout believers. In many ways much more so than people in Europe. So here we have Christians of a large number of different denomination sharing one fate. It's not very surprising that this new idea of USA as the new holy land became very popular. The constitution became almost like a new religious document that I'm sure many Christians considered divine and probably inspired by god himself. Hence, when you talk about Christianity in USA you can't separate it from nationalism and patriotism. They are deeply intertwined and dependant on each other.
I think that's why atheists are so despised in USA. They are not only seen as ungodly. They are seen as a direct threat against the very soul and soil of their nation. How can an atheist possibly be a good citizen of USA when Christianity is the very heart and soul of USA. This also explains why Christians in America are so egocentrical. When they evangelize they don't spread Christianity in the sense that perhaps most Christians from Europe do. They promote the American way of life. Because to them the American way of life. The love of the American soil is Christianity. You can't separate the American culture and politics from Christianity when you talk about USA no more than you can separate nationalism from the culture or politics. I think this is what many here don't seem to get. Christians in America don't regard atheists just as non-believers. They are a threat to the American way of life. A threat to their beloved nation. Their holy land.
So what about the issue of left/right wing politics. Well, I think it has a lot to do with the cold war. Socialism and communism were considered the big threats to USA for half a century. I think this legacy is still very much alive in the minds of most Americans. A half century of fierce propaganda is not all that easy to revise. Hence, liberalism is still seen as a threat to USA. And as such also something unchristian and unpatriotic. Hence liberals can't possibly be true Christians. They have to be atheists or in some other ways deranged individuals. Common quotes like "green on the outside, but red on the inside" demonstrates this perfectly well. Hence, the idea of USA as a capitalistic society became a vital part of the national identity and also a vital part of people's religious identity. Of course USA is not for te moment being a free market in any way. But, the delusion lives on. The market is never to be blamed for the financial situation. It can't be. Because capitalism is what makes USA so great. And as such it also becomes a vital part of people's religious beliefs. As said before you can't separate these from each other. And if the market can't be blamed then of course it has to be the government.
My point is that you can only understand Christianity in USA if you regard it as a inherent part of the cultural and political fabric of the American society. Many people make fun of the fact that many Americans are so individualistic, for the right to carry guns, warmongerers, etc. when it clearly has nothing to do with the teachings of Jesus in the New Testament. But, when you realize that Christianity in USA is to a great extent an extension of a national identity then it makes perfect sense.