Shewmaker wrote the following...

There is no such thing as "state citizenship" in the USA. Citizenship exists as a national legal concept in the US only.

This is just wrong, the Constitution of the United States says the following:

All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.

So, yes, citizens of the US are both citizens of the Nation and citizens of the State in which they reside.