Most, if not all, States have adopted English as the official language. Yet this has not stopped the use of Spanish in many State government offices. I am not sure that this will help on the national scale.
Just on a side note, the whole Mexican immigration issue is interesting to me because I am an American living in another country. Here in Austria there are a lot of Turkish people, and people from the Balkans, and everyone must speak German. When dealing with anything in the government you need to speak German, if not they tell you to learn and come back. I was never for this kind of thing in the US, but now that I have experienced it I think it is a good idea. The problem with not learning the language of the land is that one will never become part of society as a whole. You find small immigrant areas in every country. Often few speak the country�s language and never leave these small communities. Pandering to these legal and illegal immigrants by offering government services in anything other than the language of the land, only gives people one more reason not to integrate into society.
