It’s always amusing when claims are made that the United States was founded on Christian principles or that the United States is a Christian nation, Protestant or otherwise.
The United States was founded on Enlightenment values, not Christian ones. Your founding fathers were deists and even Masons. Some were Protestant. Some were even Catholic Christians.
Just goes to show that the United States founding cut across confessional and belief lines. For better or for worse, but don’t make any pretenses that the United States was founded as a Christian state or is one today. It was, from the beginning, a secular, Enlightenment state, and that remains the case today. A lot of your founding Fathers treated God as an impersonal, apathetic force, and this is pretty much still the attitude of the United States today, as a state. In God you (as a state, not individual Americans) may trust, but God you do not love, nor do you believe that God loves you. As a matter of state policy, that is.
And you don’t have to take my word for it. Read your own founding documents. Your Declaration of Independence and 1788 Constitution is dripping with secular and Enlightenment philosophy. Your heroes include men like Thomas Paine. Granted some of it is compatible with Christianity. A lot of it is even good, very good. But they themselves are not Christian documents.