The problem with the American experiment is that it is a nation built on the idea of "a people" rather than the reality of a people. What I mean by that is, you go to Italy, for example, and for the most part, it's populated by Italians. Go to Germany and it's populated, mostly, by Germans. Spain, mostly by Spaniards. I'm simplifying, of course, and thinking in terms of long-term (many generations) inhabitants rather than relatively recent immigrants. So their "tribe," so to speak, is "Italian," "German," "Spanish", etc. (Interestingly, this concept is not the case in France. I've driven through France several times, and thanks to expansion and acquisition, there are people within the borders of France who are from other "tribes." Anywhere east of Aix-en-Provence, the people are Italians (they still call Nice "Nizza"), anywhere west of Arles they are Spanish (from the defunct Hispanic kingdom of Catalan). In Alsace, they're German, and speak French with a delightful German accent. In Brittany, they're genetically identical to the Welsh. But I digress.) But my point is this: these nations have an actual national identity that gives them their tribal definition. In America, we are all immigrants, so our "tribal" definition is based on the "idea of America."
And when that "idea of America" starts to implode, as it has in recent years, and we no longer think of ourselves as "one nation" (under God or not), then we are pulled by centrifugal forces into odd new "tribal" configurations that are not based on genetics or race or a millenium of shared culture, the way it would be in Europe. Without an unwavering belief in the "idea of America," we Americans quite simply don't know what we are.