I am teaching a course on Religion and Politics in American culture. And the truth is, there has never been a time when Christianity was not used, in some sense, to validate the legitimacy of the United States Government. There has always been some large faction in American Politics which equated being American with being Christian in some sense. And on occasion, we have wrapped the American Flag quite tightly around the cross to validate the righteousness of our cause over and against that of some other nation or faction, whether in the Revolution, the Civil War, WWI, WWII, the Cold War conflicts, or the never ending "War on Terror".
What is relatively new this political season is that, in the absence of a war or clear external threat to our country, we have major preachers such as Pat Robertson and others, declaring that our sitting President is God's anointed leader and savior of the Country, and that disagreeing with him is "revolting against God". This is an interesting twist, and harkens back to versions of Imperial Christianity in the middle ages which stressed the "Divine Right of Kings" to rule as God's chosen instruments. And it brings to mind the Imperial Christianity of 1930's Germany that also anointed Adolf Hitler as Germany's savior.