Nativism is a rear-guard reaction by declining sectors of the old elite. It does not work.
Multiculturalism is a rear-guard action by declining sectors of assimilating minorities. It does not work, either.
The great American melting pot works relentlessly to turn the middle of American society into Americans. Our culture is changed somewhat by each group it assimilates, but is more continuous than changed.
And this is a good thing.