Texas would be the 14th largest economy in the world the day it seceded before it started keeping the 80 cents of every dollar that gets sent to Washington. And I seriously doubt Texas would put up with unfettered illegal immigration, massive entitlement programs and inner city poverty pimps busing ineligible voters to the polls.
There would be no cohesiveness and the remaining states would tax the crap out of the separatists.
I'm thinking your not understanding the concept. Taxing across national boundaries is pretty hard to pull off.
I was speaking of tariffs to take things across borders. It would be insane, the seceded states would have higher tariffs than China to take items across.