Is America a Christian Nation?

No. Although it is a nation with a lot of Christians.  

Recently Robert Jeffress, pastor of First Baptist Church of Dallas, as well as many other evangelicals have sought to assert that the United States was founded as a Christian nation. Their arguments are a tissue of half-truths and misrepresentations, but need to be addressed. 

https://ptv.org/america-is-a-christian-nation/ will give you as much insight as you wish into the way in which Jeffress frames his argument.

Assertion 1: "52 out of the 55 signers of the constitution, the framers of the constitution, were evangelical believers.”Clearly this argument turns on the anachronistic application of the modern term “evangelical” to men who lived over 200 years ago, before the term was ever used. So what about the founding fathers in context? If we turn to Encyclopedia Britannica we find a more nuanced answer that is far from Jeffress’ assertions. https://www.britannica.com/topic/The-Founding-Fathers-Deism-and-Christianity-1272214. And for scholarly depth one could go to The Faiths of the Founding Fathers, by David Holmes, which finds the majority to had been influenced by or were openly Diests. Those looking for a vigorously conservative view see a Heritage Foundation article at: https://www.heritage.org/political-process/report/did-america-have-christian-founding. 

Adherants.com gives us the definitive answer by listing the religious affiliations of the 55 signers:  

• Episcopalian/Anglican.      57.1%.  32
• Congregationalist               23.2%.  13      
• Presbyterian                        21.4%.  12
• Quaker                                  3.6%.   2
• Unitarian/Universalist          3.6%    2
• Catholic.                               1.8%.   1

Now Jeffress himself has said that Catholics are not Christians. Unitarians deny the divinity of Christ, so they aren’t in. And Quakers were executed for heresy in Puritan Boston, so its hard to see them being “Evangelical Christians.” Already we have 5 non-evangelical Christians. Of those remaining we know at least a few were openly Deist. So by the most general possible count Jeffress is dead wrong. If we consider that the evangelical revivals of the period were precisely intended to convert Anglicans to true Christianity his assertion becomes even more dubious. And after all, Anglicans, Congregationalists, and Presbyterians would become the bulwark for liberal protestantism. One can see that there are no Baptists, Pentacostals, Independent Evangelicals and etc. None of the groups we associate with modern Evangelicalism were present for the founding of the United States. 

Jeffress' claim is completely bogus. 

Assertion 2: The establishment clause of the US constitution isn’t intended to prevent a the government from establishing a religion, it is intended to prevent it from establishing  “a denomination.” Or to quote Jeffress directly concerning Thomas Jefferson’s writing in 1802, "Jefferson was referring to an establishment of a denomination, not a religion."

First we must note that this isn’t what either the 1st Amendment or Thomas Jefferson says. The clause, which Jefferson quotes, says “religion.” A good literalist like Jeffress should recognize that you can’t just willy nilly say that a word means something different from what it says. 

Secondly, and more importantly for those interested in the truth instead of plausible lies, is that the word “denomination” is first used to refer to a particular religious sect is 1716. That is more than 50 years before the Declaration of Independence. So if the founding fathers meant “denomination” they certainly had the word available to them. And indeed, the US Congress specifically REJECTED using the terms “denomination” and “sect” in early versions of the Bill of Rights. So Jeffress’ assertion here is completely specious. 

Why, one wonders at this point in history, is a knowledgeable religious leader asserting that “America is a Christian Nation” and then offering bogus evidence he attributes to its founding fathers and founding document? One is tempted to ascribe political motives, but with a Supreme Court made entirely of Catholics and Jews, who are excluded by Jeffress from being included in our “Christian Nation,” that seems far-fetched. Its not likely efforts to twist the constitution toward theocracy will get past them, and one wonders what Jeffress and his allies make of the fact that the Supreme Court of a "Christian Nation" doesn't have a single person they regard as a Christian. 

The more likely explanation is far more tragic. Jeffress and his constituents sense that their long standing fable of America as a preserve of evangelical Christian power is rapidly being exposed as a fantasy. The sermons and videos are an effort to reassure the nervous faithful. And the religio-patriotic mega-rallies, billboards, political prayer meetings, and increasingly bombastic self-assertion are the last colorful gasp of a dying religious star. They are a fireworks finale soon to fade into drifting smoke behind their smoke and mirrors leader. 

Fortunately what will remain will be the authentic gospel of Jesus Christ. It will be much diminished in political and cultural power, and far more like salt and light.