A senior Republican has called a party colleague running for office in Texas “a bigot” over a racist social media post attacking college football fans – and said he is so outraged by the comments that he will vote for the candidate’s Democratic rival.

Karl Rove, who was former president George W Bush’s longtime political adviser and is a respected Republican consultant in Texas, told a private event in Austin on Sunday that he could not support Bo French’s candidacy for a seat on the state’s railroad commission, the Texas Tribune reported.

Instead, he said, he will vote for Houston Democrat Jon Rosenthal over French, breaking a 32-year run of exclusively backing Republicans.

His decision came after French posted on X a photograph of students wearing team attire celebrating the University of Texas’s rousing college football victory over top-ranked Ohio State on Saturday. The students are all non-Caucasian, and French wrote: “I heard UT graduation this year looked like this. I didn’t believe it. The problem is now obviously far worse than anyone imagined.”

French could not have known the nationality or status of the students. According to Texas Global, fewer than 10% of the university’s 55,000 enrolled students are from overseas.

His framing without evidence of the Asian students as “foreigners” – and attempt to denigrate them as outsiders – reflects a growing encroachment of formerly fringe views into mainstream Republican politics nationwide.

But it drew condemnation from some in the party.

John Cornyn – the establishment Republican Texas senator who lost his re-election primary to Ken Paxton, the Donald Trump-endorsed, scandal ridden state attorney general in May – attacked French on X on Tuesday.

“The Republican Party is better than this. We should all condemn this bigotry directed at our fellow Texans or we will soon find ourselves a minority party,” he wrote, after French followed up his original post with an attempt to fundraise off it.

Even Greg Abbott, the hard right Texas governor, appeared to have reservations. “That is not my message,” Abbott told Politico. “A selective picture of Longhorn fans celebrating our biggest home victory-ever actually shows a way that Texans unite. We all support our college football teams.

“The way we win the state is the same way we win football games. We unite under the brand of Texas.”

Republican state senator Lacey Hull urged French to remove the post on her own social media feed. “This post breaks my heart. I see college kids cheering on their football team. I see Texans,” she wrote.

The chair of the university’s board of regents, Kevin Eltife, said in a statement that he too saw only Longhorns, the nickname of the college’s sports teams.

“It’s the same remarkable view I have at graduation ceremonies and anytime I’m on campus,” he wrote. “I’m proud to celebrate all our Longhorn students today and every day. Thank you for making us proud.”

French’s unashamed approach to the scandal continued on Monday in an appearance on a radio show in which he labelled Republicans who have criticized him as “less conservative”.

“The establishment raised and spent $7[m] against me in the primary,” he told host Mark Davis, reported by the Tribune.

“Many of the people who criticized me yesterday were some of the same people involved in that effort. It’s no surprise that the less-conservative people in Texas are the ones attacking me.”

Other Republicans in midterm races elsewhere have also come under scrutiny for extremist, racist or misogynistic messaging, or their backgrounds.

Brandon Herrera, a Texas candidate for a House seat in November, was called out for offensive sexual comments he reportedly made on social media using the handle “the AK guy”, a rightwing alter ego.

In 2020, Herrera, who has 4 million followers on YouTube, filmed himself firing a gun at bottles of ranch dressing and, after they exploded, rubbed the condiment on to himself and declared that this would “make me irresistible to the fat bitches”.

In 2024, after he described a Nazi-era gun as “the original ghetto blaster”, the Republican Jewish Coalition condemned him as “a goose-stepping extremist”.

In New York, Peter Oberacker, a Republican state senator running for a congressional seat, was forced to delete a Facebook post paying tribute to his grandfather, who served in Adolf Hitler’s Nazi military during the second world war.

Oberacker’s post featured a photograph of Ludwig Oberacker, who was killed during the Battle of the Bulge, in Nazi uniform. “I salute all who served,” Oberacker wrote, adding that he had debated whether or not to make the post.

In Florida, Republican US House candidate Marshall Rowson was challenged on his ties to the League of the South, a white supremacist group.

The online Talking Points Memo reported Monday that Rowson marched with neo-Nazis at the 2017 Charlottesville Unite the Right rally, at which Heather Heyer, a counter-protester, was killed.

The outlet said it reviewed video showing Rowson and his now-wife arriving at the rally and being greeted by name by members of the League of the South members, which advocates for the secession from the US of southern states.

Rowson did not respond to a request for comment after the Washington Post amplified the story on Tuesday.