Gee, really?
Texas seceded from the Union in 1861 and the Union - the USA - proceeded to conduct a vicious war against Texans which denied that they had the right to secede....which they had just done to Mexico in 1836.
Texas has been a republic once before in history. No reason they couldn't do it again.
Didn't Texas rebel from Mexico? Had a war of independence? The whole Alamo thing?