For most of it's History, Texas voted for and was run by Democrats. When the Socialist Liberals began to seize control of the Democrat Party (late 60's), the citizens of Texas began to defect from the Democrats and vote Republican.
A Texas Republican is not what folks normally consider a Republican to be. They are Socially Conservative.......God, family, Country, but more liberal in Business Policies.
Classic case in point is the Bush Family. In truth, they are more Blue Dog Democrat than Republican, and more Centrist than Conservative. Now, to be sure, there are Strongholds of far left Liberals in the larger Cities.........Houston classic example, and there are Strongholds of ultra-Conservatives as well.
It's a big State, with many different leanings............and while they once were staunch supporters of God, Family, Country, even that is beginning to slip away. Soon, Texas will be a Brown State, and as to which way it leans Politically, we will have to wait and see.