The 23rd District in Texas is a judicial creation two times over. The district was represented for over a decade by Republican Henry Bonilla, but in 2006 the U.S. Supreme Court declared that the 23rd violated the Voting Rights Act of 1965. A federal judge substantially increased the Hispanic population of the district, and Bonilla lost to Democrat Ciro Rodriguez (who had been upset in a primary by Henry Cuellar in the neighboring 28th District a few years earlier).
Rodriguez then lost to Republican Francisco “Quico” Canseco in the 2010 landslide. The GOP attempted to shore up the district, which stretches across the vast, empty expanses of southwest Texas, to bring together the Hispanic populations of the El Paso and San Antonio suburbs. But a federal court undid that effort, and actually made the 23rd a touch more Democratic than it had been in its earlier iteration. Pete Gallego defeated Canseco in 2012. Canseco sought a rematch in 2014, but lost the Republican primary to former CIA officer William Hurd.
The district still leans a bit toward the Republicans, even in presidential years, and lower Hispanic turnout in a midterm election could hurt Gallego. But Hurd might be a touch too far to the right for the district. This is the only real competitive race in Texas this cycle, so expect it to draw plenty of attention.