It's the broad public knowledge, or intuition, in America, that we are not assimilating our immigrants patriotically. And if you don't do that, you'll lose it all.
I think if one takes a look back through our history, they would see immigrants have almost never joined this country and immediately dropped their ties with their country of origin and wrapped themselves in Old Glory. I know from personal experience that my Norwegian ancestors who settled in northern Minnesota have clung very firmly to their Norwegian roots (to include speaking the language). Take a look around southern New Jersey and you see more Irish and Italian flags than American flags, and it has always been that way. The Little Italy's and Chinatowns that exist in every major American city are not a new phenomena. Neither are groups like the Pennsylvania Dutch and the Germans in Iowa. And the Cajuns down in Louisiana aren't speaking the Queen's English. The fact is, we tend to look at history in glasses tinted the color we want them to be, rather than with clear lenses. And times aren't as different now as we imagine them to be.