Winegarner, the industry affairs director for the Texas Cattle Feeders Association, led the race with 39 percent of the vote.
Jackson, who has served as a White House physician under the past three administrations, trailed behind at 20 percent of the vote.
Chris Ekstrom, a businessman and prominent donor to conservative candidates, followed in third with 15 percent of the vote.
Each of the three candidates benefited from different strengths and endorsements from prominent officials.
Ekstrom had the support of the House Freedom Caucus and Jackson had some support from President Trump, who took to Twitter to sway voters toward his former doctor.
But with the endorsement from Thornberry, Winegarner appears to be positioned as the stronger of the two candidates going into the runoff.
Given that the district is the most Republican in the country according to the Cook Partisan Voting Index, the GOP nominee is expected to be the next congressman in Washington, D.C. for the panhandle region.
However, there was still a competitive Democratic primary race for the seat, leading to a runoff between Gus Trujillo and Greg Sagan.
Trujillo, who once interned for Thornberry in D.C., received 42 percent of the vote. Sagan, a retired management consultant, received 35 percent of the vote.
The runoff election for both parties will be on May 26.
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Daniel Friend is the Marketing and Media Manager for The Texan. After graduating with a double-major in Political Science and Humanities, he wrote for The Texan as a reporter through June 2022. In his spare time, you're likely to find him working on The Testimony of Calvin Lewis, an Abolition of Man-inspired novel and theatrical podcast.