Google: But Texas is not among these “solid Republican” states nor the “leaning Republican” states (states where the party gap is between 5 and 10 percent). Instead Texas is among the 18 competitive states, with Republicans holding a 3.9 percent advantage over Democrats.Feb 18, 2015
I think it's amazing that the GOP got into the state at all.
I think what caused a lot of democrats to switch was the moral breakdown of their party. They were social conservatives.