Yes, but perhaps not in the fashion you may expect.
The US IS a predominately Christian-laden nation of self-described "Christians" (over 70%; the % number varies by source).
Yet, that percentage IS declining. More and more "Americans" today do not affiliate with any specific "church" or methodology of worship/adherence as dictated by a specific "belief". Most citizens in the US will still proclaim a "belief" in a "higher power/authority"...but decline to see themselves as "religious". Obviously, demographics play a large part in this overall estimation, skewed primarily towards younger folks as trending evermore "heathen".
As Thomas Jefferson himself acknowledged centuries before, it is not imprudent to follow the "teachings" of the alleged Jewish prophet called Jesus the Christ, but any attributions of a divine capacity or resident divine origin, were...*ahem*, foolish.
"Christians" have been here since the founding of our nation, but not to exclusion, nor even to a presiding majority of voice. The irony of this nation's founding lives within a very simple fact. Many, (if not most) of European decent (as immigrants) came here to escape religious persecution. This flaw of imposed specific religiosity (as a matter of law) inspired many others of differing faiths and beliefs to escape imposition of any personalized "faith" as civic (and even criminal) "law".
Obviously, this perspective of open and free practice of "religion", thusly allowed the expression of any and all faith-based "beliefs", even those that held NO religiosity/practices/adherence at all.
IN short, the USA is NOT a "Christian Nation". But by sheer numbers alone, the USA is predominately a "Nation of Christians". It just IS. But take heart...those numbers are consistently dwindling, and have been for decades now.