Samuel P. Huntington, in this long article for Foreign Policy, (an excerpt from his new book) argues this:
"The persistent inflow of Hispanic immigrants threatens to divide the United States into two peoples, two cultures, and two languages. Unlike past immigrant groups, Mexicans and other Latinos have not assimilated into mainstream U.S. culture, forming instead their own political and linguistic enclaves—from Los Angeles to Miami—and rejecting the Anglo-Protestant values that built the American dream. The United States ignores this challenge at its peril."
And here is David Brooks’ comments on Huntington’s theme, in today’s New York Times. Brooks thinks that our integration machinery is broken. Read both. 
Brooks is off base when he tell us the integration machine is broken.
It has been turned off by the lefty multi-culti’s who see nothing good in America or its’ history.
I would venture to guess the majority of immigrants who have become American citizens have a better understanding of this Nation’s history and goals than the majority of natural born citizens under the age of 60.