Culture isn't artificial, but lines in the sand create hard disconnects where culture is much more fluid. I'm a Seattlite, and I can tell you I feel more cultural similarity to British Columbians than I do to Texans. And people from Miami have a lot more cultural similarity to Cubans and Veneuzuelans than they do Alabamans. And Guatamalans have a ton of cultural similarity to Hondurans and Salvadorans, but northern Mexico might as well be Thailand to them. Cultures didn't define our borders, Manifest Destiny did...and cultures transcended those borders.

We have a 250 year precedent as an immigrant nation. We have always been at least somewhat tolerant of massive waves of migration, whether they were Germans, Italians, Irish, British, Chinese, etc. We have already lost any claim that our borders are lines in the sand for our socioethnic culture.

The only aspect of "American" culture that seems to be represented by our borders is a love of capitalism. And considering the fact that you can't really have capitalism with restricted trade and restricted movement of labor, it seems to me that Trump is more of a cultural invader than Salvadorans are.