Texas Rep. Dan Crenshaw owes his defeat in this week's Republican primary to a billionaire megadonor who was hellbent on ending Crenshaw's career, sources tell Axios. Why it matters: Texas banker Robert Marling 's role in funding an anti-Crenshaw advertising blitz starkly illustrates how a lone billionaire can banish a member of Congress. In this case, Marling's clout meant Crenshaw was the first House incumbent to be ousted in 2026. Crenshaw lost to Texas state Rep. Steve Toth , a hard-line conservative who doesn't have Crenshaw's independent streak. Zoom out: Marling donated $675,000 in the GOP primary, accounting for roughly two-thirds of the amount spent by a super PAC opposed to Crenshaw. Marling's contributions bankrolled a stream of mailers and TV ads that have inundated Crenshaw's southeastern Texas district since the beginning of the year. Marling — a prolific donor to President Trump and conservative causes — played a "massive" role in the race, one person involved in the primary told Axios. "Short of Robert's involvement, Dan would be reelected," said another. The backstory: There's an ongoing feud between the Crenshaw and Marling camps — and a dispute about how it began. Sources close to Marling say it started several years ago, when he invited Crenshaw to appear at an annual conservative youth summit. Crenshaw said he would speak only if audience members wore masks, so the story goes, and Marling said no. (A person close to Crenshaw denies this happened.) Then, a year ago, Crenshaw told a person close to Marling that he wanted to put Marling's "head through a wall." (Crenshaw's team also denies this.) A Crenshaw ally said the bad blood has to do with the peculiarities of Texas' 2nd District — specifically that Crenshaw represents the Harris County (Houston) portion of the district, and Marling resides in the Montgomery County portion, in Houston's northern suburbs. This source said there's been a rivalry between the two counties, and that Marling wanted the district's representative to be from Montgomery County, which he found in Toth. Others point to ideology : Marling simply didn't regard Crenshaw as conservative enough, they say. Neither Marling nor Crenshaw would comment. Zoom in: In December, a strategist from a pro-Toth super PAC visited Marling, asked for a $250,000 donation and outlined how the money would be spent. Marling said yes. Marling cut a $25,000 check in January, and another for $200,000 on Feb. 10. By early February, the Marling-bankrolled offensive had taken a toll on Crenshaw. The pro-Toth super PAC's polling indicated Toth had cut substantially into Crenshaw's lead. Marling also worked behind the scenes, telling people around Trump — including House Speaker Mike Johnson — that he hoped the president wouldn't endorse Crenshaw. Trump ended up not endorsing in the primary. Things then took a turn on Feb. 24, when Crenshaw took to social media to attack Marling, who he said was "funding all those slanderous mailers ... about me." Crenshaw also accused Marling's Woodforest National Bank of loaning $20 million to Colony Ridge, a residential development near Houston that conservatives say is a haven for undocumented immigrants. A person close to Marling said he wasn't involved with Woodforest at the time of the loan. Marling then struck back — launching an X account devoted to attacking Crenshaw. "Dan is feeling the pressure because he has lost his way in our district," Marling wrote. Marling cut a final $200,000 check during the last week of the primary campaign. The money funded an ad in which Texas Sen. Ted Cruz (R) endorsed Toth. Between the lines: Cruz had several reasons for getting involved in the race, including his longstanding relationship with Marling, sources familiar with Cruz's thinking told Axios. Marling has been a donor to Cruz since 2011, and was a major backer of his 2016 presidential bid. Cruz attended the funeral of Marling's daughter in 2022. "It's a family affair in Cruzworld," said one of the people involved in the primary. The Club for Growth , a conservative group Marling has funded in the past, also chipped in to run the ad. (Turning Point USA, another organization Marling has bankrolled, also backed Toth.) In the end, the primary wasn't close: Crenshaw lost to Toth, 55% to 40%. Marling was vacationing with his wife, Kim, in the Caribbean when Tuesday's results came in. "This is so great," he texted a friend.