Texas Attorney General Ken Paxton, boosted by President Donald Trump’s endorsement, has defeated four-term US Senator John Cornyn in the Republican Senate primary run-off, according to US media projections.

The result, quickly called by Fox News and CNN after polls closed on Tuesday, highlighted Trump’s continuing influence over the Republican Party and dealt a major blow to the party establishment in Washington, DC.

Cornyn, a longtime establishment conservative and former Republican whip, had represented Texas in the Senate since 2002 and entered the race as the favorite, backed by major donors and senior Republican figures. However, the senator struggled to connect with Trump’s political base.

Cornyn had previously criticized Trump and angered some conservatives by supporting bipartisan gun legislation after the 2022 Uvalde school shooting, while Paxton presented himself as one of Trump’s strongest allies. Trump’s backing reshaped the race, making Cornyn the latest Republican incumbent to lose after falling out of favor with the president.

"Tonight, we’ve come up short," Cornyn told reporters after the race was called. He added that he intended "to do so again" and had "always supported the Republican ticket."

The defeat makes Cornyn the first Republican senator from Texas to lose his party’s nomination for re-election and is likely to end his Senate career next year. "Tonight, we just made history," Paxton told cheering supporters, praising Trump’s endorsement as "the most powerful force in politics."

This month, Trump’s endorsement of Republican primary challengers ousted incumbents including Louisiana Senator Bill Cassidy and Kentucky Representative Thomas Massie. Paxton has spent years facing legal, ethical, and personal controversies, including a 2023 impeachment by the Republican-led Texas House of Representatives, allegations of bribery and misconduct, and a high-profile divorce.

The 63-year-old was later acquitted by the Texas Senate. Paxton has repeatedly dismissed the allegations against him, framing them as politically motivated attacks.