Maybe so, but then we need to come up with more words. As the UK proved, a nation in the EU is free to leave the EU, but a state in the US is not. (Without consent of the US, of course.)
Which article or amendment of the U.S. Constitution forbids a state to leave without permission of the U.S.?
And good luck finding a good vehicle to overturn that precedent.
The TEU at least provides an explicit process for leaving