Four big blue cities: The counties that are home to Texas’ four biggest cities — Houston’s Harris County, San Antonio’s Bexar County, Dallas County and Austin’s Travis County — are generally considered reliably Democrat. In 2016, Hillary Clinton defeated Trump in these counties, 57.4% to 37.6%. These areas are also adding the most new voters. Since 2016, they saw an increase of 630,796 registered voters, according to data collected by the Texas secretary of state.
Six fast-changing counties: Just outside those big cities are the fast-changing suburbs. Over the past several election cycles, these areas of the state have been slipping away from Republicans’ grip. In 2016, Fort Bend County flipped blue. In 2018, Williamson and Hays voted Democrat. Collin County and Denton County have remained red — but some believe they may be in play for Democrats in 2020.