There is of course no clause of the constitution that forbids secession but SCOTUS currently interprets the constitution as creating an "indestructible union" i

There is of course no clause of the constitution that forbids secession but SCOTUS currently interprets the constitution as creating an "indestructible union" if I recall the language correctly. And good luck finding a good vehicle to overturn that precedent. The TEU at least provides an explicit process for leaving