The incumbent Greg Casar, a former Austin councilman, seeks a second term in Congress. He did not face a primary challenge.
Texas 35th Congressional District, which spans from San Antonio to Austin along I-35, is heavily Democratic.
On the Republican side, veteran Michael Rodriguez faced retired Kern County, California, deputy sheriff Steven Wright to see who will challenge Casar in November.
By 11:00 p.m., this race was too close to call.
Republican John Kuempel of Seguin was one of the eight GOP incumbents being targeted on primary runoff night by Gov. Greg Abbott over opposition to school vouchers.
Kuempel was defeated by software executive Alan Schoolcraft.
The district, which runs east of San Antonio, covers Seguin and Gonzales.
Schoolcraft had 55% of the vote to Kuempel's 44%.
Kuempel was one of six GOP incumbents who lost their races on Tuesday. Abbott said he "now has enough votes to pass school choice."
Former Uvalde mayor Don McLaughlin Jr. won the Republican primary for House District 80 with 58% of the total vote.
McLaughlin gained international attention for serving as mayor of Uvalde in the wake of the 2022 Robb Elementary School shooting. He resigned to run for the seat that Democrat Tracy King has held since 1994.
On the Democratic ballot, Cecelia Castellano won 57% of Tuesday's runoff vote while Rosie Cuellar garnered 42%. Cuellar is a former Webb County tax assessor and sister of U.S. Rep. Henry Cuellar.
The matchup is now set for November between McLaughlin and Castellano.
District 80 covers six counties: Uvalde, Zavala, Frio, Atascosa, Dimmit and Webb.
KUT's Lauren McGaughy and Houston Public Media's Andrew Schneider contributed to this report.
