The Founders were pretty clear about leaving tribalism's recessed brow in the historical outhouse, even to the extent of writing democracy preventatives into the Constitution.
A lot of people try to retroactively write their tribe into it, so they can claim to be "every bit as American" as the Posterity whose rights the U.S. Constitution was written to protect. To cite one phrase of a document in contradiction to the central theme of the entire document (what civic nationalists tend to do) which is that the People of the United Colonies are an English people, unique and distinct from foreigners, Indians, and the English people loyal to the King of Britain, is an outrageous attempt at deceit that relies entirely on the historical ignorance of the audience. To say that anyone can become an American because "all men are created equal" is a shameless lie. One might as readily cite it as evidence to claim it means anyone can become Chinese.
But, like I said, civic nationalism has an element of truth underlying it. Washington wrote a letter to a group of Dutch, encouraging them to come to America, saying it's his dream that it'll become a welcoming place for all the oppressed people in the world who want to be free.
It's a nice ideal, sure, but it's all in the past, the important thing is that now we know magic dirt doesn't work. It's very clear that assimilation doesn't happen, and even more so, it hasn't happened with the early waves of immigration, that are often cited as having been successful. Civic nationalism is an utopian vision, like libertarianism, like communism. And people get wrapped up in the rhetoric. They're emotionally attached to this idea, and worse they feel like they're hating on their immigrant friend if they reject it. But macro is not micro. And whether people like it or not, it simply doesn't work. That's what really matters, it does not work.
The truth is, Diversity + Proximity = War, and if you don't understand that I suggest you to read Martin Van Creveld.