text: So you think secession is legal?
  Based on what?
  
  The "...argument against secession centers on the language of Article I, Section 10, which declares that “No state shall enter into any treaty, alliance, or confederation….” To proponents of this position, Article I, Section 10 unequivocally shows that the states which formed the Confederate States of America were in clear violation of the Constitution, thus invalidating their government and the individual acts of secession which led to it. Abraham Lincoln indirectly defended this position by declaring the seceding states were in “rebellion” and therefore still members of the Union. The Constitution, then, was still legally enforceable in those states, including Article I, Section 10."
  http://www.theamericanconservative.com/articles/is-secession-legal/
  
  Given the choice of Lincoln, or a kon man, I'll go with Lincoln every time.