I don't know if it's legally possible, but even if it was, it would never actually work. Texas is propped up with federal funding, our electric grid is slowly failing, and most people who wanted to stay a citizen of the United States would leave if they were able, which would completely fuck the job market, and leave mostly people who want to be Texans rather than Americans, and those people can't run shit (hence the economicand infrastructure problems we already have). Or maybe I'm just talking out of my ass, idk. That's my opinion as somebody who lives in Texas against their will.