On July 17, 2013, Texas attorney general Greg Abbott, having recently declared his candidacy for the Republican gubernatorial nomination, hosted a town hall on Twitter. The exercise was, perhaps, poorly timed.

For 20 years, the Texas Democratic party had been in the wilderness. In recent years, though, national Democrats, casting a covetous eye at Texas and its 38 electoral votes, had dabbled in the idea that “changing demographics” would eventually turn the state blue. The phrase was general enough to cover several concurrent trends, including increasing urbanization and migration from other states, but the key issue was the growth of Texas’s …