AUSTIN, Texas – Texas Attorney General Ken Paxton is running for the U.S. Senate in a primary challenge against Republican Sen. John Cornyn, setting up what is likely to become one of the GOP’s most contentious and expensive contests of 2026.

Paxton, a close ally of President Donald Trump, announced his decision Tuesday in an interview with Fox News’ Laura Ingraham after spending more than a year openly flirting with a Senate challenge. During that time, Paxton has sought to position himself as a national leader among the GOP’s ascendant hard right, launching some of the first criminal investigations in the U.S. over abortions and gender-affirming care for transgender youth.

“I’m running for U.S. Senate to fight for President Trump’s agenda and take a sledgehammer to the D.C. establishment,” Paxton said in a post on X. “Together, let’s send John Cornyn packing.”

His decision to enter the race highlights his political resiliency and popularity among Texas Republicans after a decade of legal woes that, at times, seemed to imperil his future: felony securities fraud charges, impeachment after an extraordinary revolt by his closest aides and an FBI corruption investigation. Paxton reached a deal to end the criminal case, was acquitted in a historic impeachment trial in the Texas Senate, and the Biden administration quietly decided not to prosecute him.

Cornyn, a respected and popular senator within the GOP conference in Washington, will likely now have to face his most competitive campaign since taking office in 2002.

He recently lost his bid to lead the GOP as Senate majority leader in November after he spent several years as Sen. Mitch McConnell’s No. 2 in leadership. A former Texas attorney general and state Supreme Court justice, Cornyn has helped the party raise millions of dollars throughout his decades-long career and has worked with Democrats on bipartisan bills.

Cornyn has received criticism from Paxton and other Republicans after he suggested that Trump might not be the best Republican candidate for the 2024 presidential election.

Paxton has also expressed discontent with Cornyn’s support of a 2022 bipartisan gun bill that strengthened background checks for buyers under 21, increased prosecution for unlicensed sellers and funds for youth mental health services in the wake of the Uvalde, Texas, elementary school shooting that killed 19 children and two teachers.

Amidst several legal battles, the Texas attorney general has become a well-known figure on the right for his litigation against former President Joe Biden. Notably, Paxton led a lawsuit attempting to overturn Trump’s loss to Biden in 2020, an effort that the U.S. Supreme Court rejected.

In 2023, the Texas House voted to impeach Paxton for bribery offenses related to a wealthy real estate donor. He was later acquitted in the Senate following a two-week trial. The Justice Department decided not to pursue its investigation into Paxton over the allegations in the final weeks of former President Biden’s term, according to two people familiar with the matter who spoke to The Associated Press on the condition of anonymity.

A district court judge in April awarded $6.6 million combined to four former senior Paxton aides in their lawsuit against his office after they were fired shortly after reporting Paxton’s office to the FBI for bribery allegations.

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Associated Press writers Alanna Durkin Richer and Eric Tucker in Washington contributed to this report.

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Nadia Lathan is a corps member for The Associated Press/Report for America Statehouse News Initiative. Report for America is a nonprofit national service program that places journalists in local newsrooms to report on undercovered issues.