Actually, at one time, HOuston and Dallas were the only red places on the Texas map. And these days, metro Houston is more GOP than metro Dallas. The big swing red is in rural Texas. It used to be said, as rural Texas goes, so goes the nation. No more.
That is true about rural Texas, but Houston is *still* more liberal than Dallas is. Dallas proper is liberal, but all the suburbs (where most people live) is very conservative.
Dallas surrounds two small cities - University Park and Highland Park. The former is the richest suburb (per capita) in the area, if memory serves, and the latter (which is the next richest) is the #1 zip code for Class III (machine gun) firearm ownership in the United States.