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.
Nope, it's not possible. The only way it wouldn't be treason is if all states agree, or if they start a revolution and are successful; every other attempt would simply be treason. Hence, one nation indivisible. I'm sure they know that; they just want to push as far as they can to make the political situation even more absurd in America. They want to widen the gap between the people. I don't know who exactly profits from this situation, but it's not the American people.
The EU had a documented process for a member state to leave. It was untested and messy, but it existed.
There's no legal basis for a state to leave the US. Now it's possible we let it happen despite this, with or without armed conflict, but it's hard to imagine a hypothetical Texit not being messier than Brexit ever was