The actual fighting in the Civil War began over precisely this issue, with the Yankee govt. claiming that it had a right to maintain a fortress (Ft. Sumpter) within a major seaport of a newly-independent State.
It would be almost impossible to form a new Confederacy today, because there are statist colonies (e.g. Austin, TX) within even the most freedom- and secessionist-minded States. There is an 0bammunist Fifth Column everywhere. 0bama could simply order the U.S. military to reconquer the liberated territories, as his hero Lincoln did.
So I guess our founders who really only had between 33%-50% of the population at one time shouldn’t have tried either..