There is no doubt that the United States is a predominantly religious country. The most recent survey by the Pew Research Center on religion in America showed that about 83.9% of Americans identify themselves with a religion (while only 16.1% do not). And the predominant religion in this country is christianity -- which 78.4% of the population say they identify with.
With impressive statistics like that, it's easy to see why the religious fundamentalists think they should be able to force their religion on everyone in this country. But the picture is a lot more complicated than that. For one thing, the evangelicals do not make up anywhere near half of the American population (and still fall short even when the Catholics, who have been siding with them more and more, are added in). Second, their indulgence in politics and hate are turning many religious people off (and driving them out of the churches).
This turning away from organized religion has been going on for many years now, and each generation from the "Greatest generation" to the "Millenials" has shown greater percentages turning away. And it's not just the Pew surveys that show this. The Gallup Poll has been polling Americans on religion since about 1973 -- and back then about 66% to 68% of Americans said they had a great deal of confidence in churches/organized religion. But it is not that way anymore.
The most recent Gallup Poll that asked Americans if they had a lot of confidence in churches/ organized religion show a record low percentage saying yes -- only 44%, or significantly less than half of the population. This doesn't mean the other 56% of the public no longer consider themselves to be religious. In fact, most of them are religious (remember only about 16% of the total population have no religious affiliation at all). They have not necessarily abandoned their religion -- only the organized aspects of it, like the churches.
As an atheist, I naturally would like to think that these people have lost their faith, but the truth is that most are just turned off by the churches and other religious organizations involving themselves in politics (as though their god had decided that one U.S. political party was preferable over all the others). This is especially true of the churches that seem to have abandoned the christian message of love for a political message of hate.
The religious right may actually think they are doing god's work by involving their churches in political causes, but what they are really doing is driving away many of their own members -- people who want to remain christian, but can no longer stomach the hate-filled politics of their organized church.