>>518693343 (OP)
Trick question, they don't have one.
They have hundreds of national identities.
"USA" and its Constitution are ideas and ideals, anyone can become a citizen under them.
That means that any culture and indeed almost every culture has at one point been American or is American now.
As a consequence, the concept of American is integrally devoid of meaning, and Americans know that.
That's why they never just call themselves American when speaking of their own identity. They call themselves Irish-American, English-American, French-American, African-American.
That's because if you try to find someone uniquely American in the realm of cultural products and traditions, there's only 1 category you're going to find: product/service brands that were created there.
But that's not really culture.
What about sports? All practiced elsewhere before Americans made a new brand and called it that.
So no, there is no American national identity.
It's fictitious and rootless.