Presumably this question focuses on the right of individual States to withdraw, and the answer to that question is two-fold. There is nothing in The Constitution that specifically prohibits withdrawl of a State from the apparently voluntary union. The Civil War made a de facto change in that principle. There has, however, never been a de jure change. In its articles of stathood, Texas was given a specific right to withdraw although since it was part of the Confederacy and "re-admitted" that "right" is perhaps arguable. On the other hand, the Union did not recognize the right of the confedersate States to withdraw. If they couldn't "withdraw," they couldn't be "re-admitted." But the larger question still looms. And in view of the invasion from South of the Rio Grande Border and the shift of political power it will eventually bring about, we may be faced with the withdrawl of Arizona, New Mexico and California and their "reunion" with Mexico. What then? The fundamental principle should be voluntary union; voluntary withdrawl. That would revive some hint of the so-called "federal system."