Americans are blessed. Certainly, Christians can live, have lived, and do now live under a variety of governmental systems; and true Christianity thrives particularly in times of persecution, because its adherents cling only more closely to its founder, Jesus: Paul declared, 2 Cor 12:10, "Therefore I am well content with weaknesses, with insults, with distresses, with persecutions, with difficulties, for Christ's sake; for when I am weak, then I am strong."
However, while scripture teaches that authority, and therefore, government, comes from God, Rom 13:1, the fact is that not all governments (or governmental systems, such as communism) are godly. A nation (or its government) can be characterized as righteous or sinful—Prov 14:34, "Righteousness exalts a nation, But sin is a disgrace to any people." This is often reflected in a nation's laws: "The ultimate sanction of law rests on the righteous authority of the Almighty," (Calvin Coolidge, 30th US president). Law, absent the authority of God, is unrighteous.
Righteousness or sinfulness can also be reflected in the thinking of a nation's founders. In a speech given on the 150th anniversary of the Declaration of Independence, Coolidge noted that to understand why the founding fathers chose the course of action they did, "We must think the thoughts which they thought. Their intellectual life centered around the meetinghouse. They were intent upon religious worship. While there were always among them men of deep learning, and later those who had comparatively large possessions, the mind of the people was not so much engrossed in how much they knew, or how much they had, as in how they were going to live. While scantily provided with other literature, there was a wide acquaintance with the Scriptures. Over a period as great as that which measures the existence of our independence they were subject to this discipline not only in their religious life and educational training, but also in their political thought." In other words, the Bible was central to their thinking in all aspects of life, including politics—otherwise, they would never have appealed to the "Laws of Nature and of Nature's God": a God evident to all, whose laws are understood even by the godless, Rom 1:19,20. Nor would they have assumed it "self-evident, that all Men are created equal, [and] that they are endowed by their Creator with certain unalienable Rights," as one could expect, because, "…He made from one man every nation of mankind to live on all the face of the earth, having determined their appointed times and the boundaries of their habitation," Acts 17:26.
Coolidge warned, "We live in an age of science and of abounding accumulation of material things. These did not create our Declaration. Our Declaration created them. The things of the spirit come first. Unless we cling to that, all our material prosperity, overwhelming though it may appear, will turn to a barren scepter in our grasp. If we are to maintain the great heritage which has been bequeathed to us, we must be like-minded as the fathers who created it. We must not sink into a pagan materialism. We must cultivate the reverence which they had for the things that are holy."
There has always been a temptation to trust in wealth and our own knowledge (the word "science" literally means, "to know"), 1 Cor 1:26; Lk 10:21. And yet, God rules in the kingdom of men, Dan 5:21; He has authority, and takes action. He has "determined their appointed times and the boundaries of their habitation" for an ultimate purpose: "…that they would seek God, if perhaps they might grope for Him and find Him, though He is not far from each one of us," Acts 17:27. While thankful for abundance, and the blessings of scientific thought, they cannot become our gods. As Christians, we must seek God ourselves, and help our neighbors to find Him, as well. We must repent and turn from national sin (and there is much to repent of), pray for those in authority, and call on them to lead in a way that glorifies God, Dan 9:15,19; 1 Tim 2:1,2. And we should express thanks for His kindness in allowing us to live in such a truly exceptional nation.
—Calvin Coolidge (one of our most under-rated presidents) quotes are from his "Address at the Celebration of the 150th Anniversary of the Declaration of Independence in Philadelphia," www.presidency.ucsb.edu/node/267359