If Texas were to try a legal form of secession, the way to go about it would be to use the clause that allows them to split into five states and threaten to do this if they are not allowed to secede peacefully. Would Obama be willing to have eight more senators in the Senate appointed by a Republican governor to foul up his Senatorial fig leaf and prevent his nominations from passing? Hell, no. THAT’S how Texas can leverage their way into a peaceful secession if they were to choose to do it.
I don't think that option is any longer valid. It was part of the articles of annexation, yes, when Texas first joined the union. But when Texas re-joined the union after the Civil War, I believe that option was made null and void.
Were it still in effect, though, six other states would be in for a rude surprise -- because the original dimensions of Texas would apply. Which means that
1. Oklahoma would lose its panhandle.
2. Kansas would lose all of West Kansas north of the panhandle.
3. Nebraska would lose everything south of the North Platte River and north of the panhandle (which would include the Nebraska panhandle).
4. Wyoming would lose everything south of the North Platte and north of the source of the Rio Grande.
5. Colorado would lose everything east of the source of the Rio Grande
6. New Mexico would lose everything east of the Rio Grande.
So, not only would the new, improved Texas gain ten Senators, but four Democrat Senators in Colorado and New Mexico would be displaced.