I've been told that there were proposals to make German a second official language during a big wave of German speaking immigration, just like you hear similar proposals with Spanish during the big wave of Spanish speaking immigrants.
One problem with these is that historically bilingualism is never used to accommodate immigrants, who can be expected to learn the native's language, or for that matter not let in at all. Immigrants' languages become official only when immigrants are conquering outsiders, in which case their language becomes the MAIN official language.
Bilingualism and similar schemes is used to accommodate an already established population that speaks a minor language, which the country has annexed. The situation applies to many Spanish speaking communities in the southern portions of the US and Puerto Rico, but there were never enough to them to make it an issue. You have to increase their numbers pre-annexation, or have the US take in big chunks of Mexico as well, and add Cuba.
The other problem is that the US has never had an official language, nor have any of the states, which is probably an insurmountable barrier to a second official language.