The phrase "Christian nation" can mean different things, depending on the context. Readers of this blog know that I often say our nation has Christian roots, or perhaps Judeo-Christian roots. Readers also know that I say we were not founded with an official religion, Christian or otherwise. There are Supreme Court cases saying we are a Christian nation. There are founders who have said it. Presidents have said it. I'm sure none of those statement meant to say that our citizens are compelled to worship as Christians, much less compelled to worship as any particular Christian denomination.
"A nation which does not remember what it was yesterday, does not know what it is today, nor what it is trying to do. We are trying to do a futile thing if we do not know where we came from or what we have been about.... America was born a Christian nation. America was born to exemplify that devotion to the tenets of righteousness which are derived from the revelations of Holy Scripture."
(The above quote is found in several articles, including this one: "Is America a Christian Nation?" by Carl Pearlston)