If I am not correct please tell me, But all the southern state after the war were required to be "readmitted" as states as a condition of "Reconstruction". Doesn't that "readmittion procedure" make null and void and prior admission resolutions? Did that readmission procedure require a non secession clause? If it did require such a clause, would such a clause be unconstitutional under the 14th Amendment, which requires equal protection under the law? That what is legal, under the Constitution, for one state can not be illegal for another state.
So the question comes back to, is secession legal for any state, not just Texas?