Earlier quoted context omitted.
It is illegal for the US government to create a mandatory national identity system or coerce the States into creating one. The limits of this have been pretty thoroughly tested in the US Supreme Court. Every time things like this come up, everyone asks why don't we just thing that looks like a national identity system to fix the issue, as if that never occurred to anyone in Congress. This is why: it violates the Cons…
Things like the Real ID Act seem to be as close as we can get without constitutional changes. Something like the above could potentially be implemented like that, but still would not be as widespread as an SSN.
Prior Supreme Court cases have ruled that the Federal government cannot coerce the States, e.g. via taxation or regulatory authority, to do something for the Federal government that the Federal government is prohibited from doing itself. Without the voluntary compliance of the States, which is like herding cats, with respect to creating a national identity database, the net effect of Real ID will basically be more standardized State IDs.