For a singer-songwriter, 
Taylor Swift wrote an awkward post about voting. She said she will ‘be voting in the state of Tennessee’ rather than just Tennessee. She encouraged everyone to ‘register to vote in the state of TN’.
Whoever wrote the post for or with Taylor could have easily said Tennessee, not ‘state of Tennessee’ or ‘state of TN’. Everyone would know she is talking about the state.
The band, The Eagles, didn’t write ‘Welcome to the Hotel in the state of California’ or ‘Welcome to the Hotel of state of CA’, they wrote ‘welcome to the Hotel California‘. When talking about France, we don’t say ‘the state of France’ or ‘the country of France’, we say ‘France’.
TN refers to the federal land (or corporation) within the borders of Tennessee, the (nation) state. I fear that performers will walk on stage in Memphis and yell out, “How’s it going TN?”
The real abbreviation for Tennessee, the (nation) state, is ‘Tenn’, see diagram below.
TN is federal jurisdiction. Tennessee is state jurisdiction. Federal laws apply to TN. State laws apply to Tennessee.
The phrase ‘state of Tennessee’ where the word ‘state’ is lower case could refer to the real (nation) state of Tennessee but it is still an awkward wording for an instagram post.
On the form to register to vote, it likely asks if one is a U.S. citizen. Note that U.S. citizens are not the same as state citizens, meaning Tennesseans. U.S. citizens are people born or naturalized in the territories, such as Puerto Ricans. Taylor Swift is not a U.S. citizen, she is a Tennessean, a state citizen. She is one of the people of Tennessee.
I got this perspective from this content:
- The paper ‘Where do you think you are?‘ (PDF) and others by the same author.
- Listening to Roger Sayles
For a related post, read my introduction to this topic.
Related
- Review these slides
- Read this,
- review this diagram of US vs USofA,
- read these six PDFs,
- watch Richard McDonald's seminar intro
- learn to speak like a simple man
- If this site ever goes down, the archive is on the wayback machine.
She is just being accurate. Since the 14th Amendment was declared to be in force, the only state elections taking place are in the federal “State of XX” political subdivisions. There are no elections held in the union states any longer.