It's widely debated on whether or not Texas has the legal right to secede from the Union. Some argue that the Civil War took that right away from Texas, others argue that parts of the Texas Constitution put the ultimate decision in the hands of the people. A recent reference to Texas' right to secede in a speech by Governor Perry got a lot of people riled up.
It's a crazy idea to consider. I think Texas could fix the Mexico-Texas border problem overnight. But we would also inherit a lot more border to deal with along our other boundaries. I wonder who would get NASA? Do you think Austin would apply to be a Union province located within Texadonia? Maybe a better strategy would be to define the new Texadonia borders as the original Southwest Airlines triangle (Houston-Dallas-San Antonio) and let the US have the rest (sorry Kelly and Vanessa, just get yourself and families back inside the triangle before it's too late). I think it raises an even more fundamental question, do you consider yourself an American then a Texan or the other way around? I think it's a moot point, I don't think the US would ever let Texas leave the union anyway. They would send troops, we would fight for a few years, and then we would eventually make some kind of treaty and end up being annexed by the US again anyway. I think something really horrific would have to happen in order for the Republic of Texas to ever try and leave the Union, but never say never.