Rick Perry, Governor of Texas, seemed to threaten secession:
I'm sure Texans would realize that would be a stunningly bad idea to try to secede and as a result, it'll never happen.
Later, answering news reporters' questions, Perry suggested Texans might at some point get so fed up they would want to secede from the union, though he said he sees no reason why Texas should do that.
"There's a lot of different scenarios," Perry said. "We've got a great union. There's absolutely no reason to dissolve it. But if Washington continues to thumb their nose at the American people, you know, who knows what might come out of that. But Texas is a very unique place, and we're a pretty independent lot to boot."
But for an amusing thought experiment, let's say that the impossible came to pass and Texas announced that it was no longer part of the United States. Also assume that they made a deal with Mexico to be a trading partner and to use Mexico's ports in case the U.S. decided to do a naval blockade against the newly sorta, kinda, independent Texas.
The question is, would the U.S. being willing to do anything serious about it? I rather doubt it, especially under Obama. Sure, there'd be Congressional resolutions, and UN Security Council meetings, and people would huff and puff and blather endlessly. But I really don't see the U.S. being willing to kill a bunch of Texans followed by imposing martial law for who knows how long. Too many people in too many other states have friends and family and business interests in Texas.
In other words, I think Texas could get away with it.