America is actually a nation built of British Scotch Irish and English protestant theological and common law foundations.
What about Germans!!???!?
Ben Franklin was terrified of the German population levels in Pennsylvania and other parts of New England. He was also an ardent supporter of English as the official language of the US. There was a real possibility of German being the offiicial language of a large swathe of New England.
Later on in the 1870's we had problems with the Chinese. The chinese railworkers would do work that no american could be found to do. Work with dynamite in caves, exhausting work for low pay, etc.
All sorts of legislation was passed, some good and some bad. Ultimately, whenever cheap labor arrives to threaten american semi-skilled or unskilled labor, americans do two things:
1. invent something that makes major improvements in how jobs are done. Examples include the cotton gin, the steam engine, the combustion engine, nuclear power, assembly line production, heavy farm equipment, computers, etc.
2. train american workers to operate these devices. The demand for unskilled labor goes down again.
We have survived crises like these before and we will face them again.
I'm personally not threatened by a bunch of illiterate mestizos as far as my job is concerned. I'm mostly worried about the drain of $16 billion a year from our economy that is sent back to mexico, the money on health care they represent, the the "reconquista" of the Southwest that they advocate.