Then Mr. Perry stepped down. The succession appeared to go flawlessly — but it was harder than ever to say what exactly the Republican Party of Texas was about. The new governor, Greg Abbott, didn’t appear to want to do anything. Lt. Gov. Dan Patrick, an eccentric suburban Christian soldier who unnerved many in his own party, immediately went to war with House Speaker Joe Straus, a moderate Jewish Republican from the leafier parts of San Antonio. Attorney General Ken Paxton was quickly indicted on a charge of felony securities fraud.

Before 2014, some Republicans sought to help undocumented Texans. After, the party retreated into an increasingly grotesque nativism. Christian activists went to war with the business lobby. The state spent the better part of a year debating what bathrooms transgender kids should use. Slowly, the “serious” people in the party started heading for the door — or were thrown out the window.

Donald Trump compounded the problem — he’s outside a few of the main traditions of Texas conservatism, and he’s surprisingly unpopular in the state. Many observers credit him with the forced retreat of the Republican Party from Texas suburbs. And the tectonic drift of demographic change slowly reshaped the electorate — a booming population, especially in urban areas; new immigrant communities; younger and nonwhite voters turning away from the party. When the foundation started feeling shaky, the people at the top started wobbling. Hence Texodus.