The entire south used to be democrat. But there was LBJ and his civil and voting rights acts followed Nixon's southern strategy to bring the southern populist democrats into the GOP.
Texas Gov Rick Perry was a democrat. He didn't shift til 1990.
Texas lagged behind the rest of the south in shifting to the GOP. The first attempt at making the shift was from GHW Bush but the Texas populists detested him because he was a carpetbagging northern republican elitist.
True that. But Texans rallied to what they have always been— a Republic, which has the ability to actually leave the US, since the democrats have forgotten that the US IS a Republic.