Lets face it. Most of the "believers" who come here, bellowing about how christian they are" are obviously American.
At first glance it might be easy for someone to assume they know what you mean by "obviously American". It would nonetheless be helpufl for you to clarify the defnition you meant since it is otherwise not obvious. In the mean time, you may not be aware that the majority of Americans are transplanted Europids, probably somewhere around 10th to 20th generation by now but Europids nonetheless.
EDIT: clarification, this might be more accurately said 10th to 50th generation, depending on the lack of universal agreement on - how long between successive generations? Some people say 20 years, some 30, some 40. Frequently there is great news made out of new-born babies found discarded in garbage dumpsters. In these instances "generation" seems to be somewhat loosely defined - just a for instance, as a twelve year old girl who figurred out a way to become impregnated by an older boy.
Popular music, movies, literature etc contains almost no mention of christianity. We live in the most rapaciously capitalist society on earth. No Universal healthcare. Even Children aren't covered. Workers rights are virtually none existent. We're not even legally entitled to paid holidays.
The obvious that jumps out from this is that you seem to equate socialist's views, socialist's doctrine and socalist's methodology with Christianity. Again, try to remember the obvious Europid factor involved here that must be genuinely considered as a pevailing backdrop & influence to most things "american". Vast tracts of Europe were cobbled together into a seemless socialist society in the wreckage of of WWI and WWII. There has been credible evidence accumulating, since about the time WWII was shut down, that indicates WWIII will in part involve the same kind of new society being built out of the still-to-be-wrecked America. Also try to remember that it was the wreckage-factor that was one of the main agendas behind WWs I & II in the first place - relandscaping by fiat vast tracts of European culture into a unified, genericized socialism. This obviously explains why many of the former, independent, sovereign European nations now contributing to the seemless and still-growing EU have been accustomed to the overt ways of Socialism for many decades now. As far as the culture question "music, movies, literature", etc presently infecting the American colony, again, please refer to the mother culture, still known to frequent the haunts in and around The City, by way of Tavistock Institute. One last comment on this section, when it comes to non sequiturs, "no universal healthcare" woven into conversation purported to be premised on the question of "where's the Christianity?" is a reallllllly big Maza ball hanging out there in the middle of no where. Are you genuinely wondering where America's claim to Christianity is, or did you really mean to inquire as to why American's are still behind the global curve in implementing socialism? As far as this goes, that Americans have not, yet, accepted their government foisting socialized medical care upon them remains as one of the best of the few proofs remaining that at least some Americans still know there way around legitimate Chrisitanity.
American Christians generally believe that the country was founded on Judeo-Christian principles. This is somewhat true...
That may be somewhat true but it is otherwise mostly false, This country was founded on the principles of displaced Europids - mainly English, but with a health sprinkling of French, Spanish, German and other European flavors, who among other motives, were looking for a reason or way to get the H out of Europe where monarchy - prettied up fascism, was still the rule, where subjects were free to pursue whatever religious beliefs their ruling kings and queens dictated... or else. As far as the "founders" you speak of, you paint with a rather broad brush. The actual founders were mostly elite appointees of nobility, landed gentry, family and or close friends of nobility delegated with the royal duty to come over hear and begin the long job of harvesting by hook, crook, brutality and when those failed, by feigned niceties upon the Natives, the riches of this continent. Perhaps you failed to notice how this caliber of "founder" had at their disposal masses of peons "pilgrims" ... tools, which they were saddled with for said purpose. One must always wonder what the conditions were like at home in Europe that these masses of fleeing pilgrims were willing to risk their lives to flee all of that by sailing uncertain & wide open seas for the purpose of landing upon even less charted, un-tamed, wild territory upon arrival.
The moral to your quest of searching for where American's lost Chrisianity got to may well be found in figurring out where, how and why most of Europe seems to be excelling in the lack of same and has been doing it for far longer than those of us in this relatively new world.