There is no such thing as a Christian nation or a Christian army or a Christian bathroom. There are Christians in all three, but to say that a nation is a Christian nation is to completely misunderstand Christianity. Christianity is about life and salvation given through Christ Jesus. Did the United States declare war against Germany and Japan, or did Christ?
It is true that the Declaration of Independence based human rights on a Creator and not the state. That is not Christianity. You can believe that, and be a Jew or a Muslim. Christ did not establish any government, religious or secular.
The video does present well the history of our nation and how it was founded on Christian principles. What a difference we would see in our culture today if people chose to walk as God desires.
However,those that say America is strictly a secular nation are also deeply mistaken. The core of the "American Creed" is the assumption that God exists and bequeathed to humanity the endowment of Life, Liberty and the Pursuit of Happiness." Religion, in general, has a vital civil role. . .to provide the virtue to the populace from which the common parameters of good citizenship are derived.