Willie Nelson is playing a political concert for Beto O’Rourke. Some fans are abandoning him.

_{*Correction appended.}

On a muggy Fourth of July night just outside Austin, Rep. Beto O’Rourke walked on stage wearing a light blue button-down, with a Texas-size American flag in the background. But rather than one of his campaign rallies in his Senate bid against Republican Ted Cruz, the Democrat was in front of the thousands that came out for Willie Nelson’s Fourth of July Picnic, an annual celebration of country music started by the legendary singer 45 years ago.

Met with a mix of wild cheers and a fair share of booing on the soggy holiday, O’Rourke explained why this Independence Day mattered even more to the country, expressing hope that “the big, bold, confident, strong people of the state of Texas” would help show the rest of the United States that there’s no need to be afraid of immigrants, Muslims or anyone else who might be considered different.

“It’s my honor to be here tonight, to be able to work with so many of you,” he said just before the fireworks, “to be with legends like Ray [Wylie Hubbard] and Willie, who ensure that in times of disappointment and darkness that we meet that with power and joy and rock-and-roll music.”

Soon after, O’Rourke, whose punk-rock roots would later be rehashed by the Cruz campaign, shed his button-down for a black T-shirt and guitar and joined Nelson and the rest of his band on stage for spirited renditions of “Roll Me Up and Smoke Me When I Die” and “Will the Circle Be Unbroken” to close out the show.

For Nelson, the jam session with O’Rourke was the latest in a career filled with activism and liberal-leaning political stances that have largely gone against the norm for country-music culture.

But for some of Nelson’s fans, his partnership with O’Rourke was the breaking point. After Nelson announced Wednesday that he would be headlining a Sept. 29 rally for O’Rourke in Austin, fans have taken to social media to boycott and publicly disown the country legend.

On Nelson’s Facebook page, where he posted an article from news outlet Austin360 with the announcement, some of the most striking remarks accuse the performer of aligning with what they believe to be the “socialist” positions of O’Rourke.

“Goodbye Willie,” David R. Williams posted on Facebook. “I don’t support socialist commies! You’re not going to advertise on my FB page either.” He added: “Like we say in Texas, Now Git.”

“Open your eyes Willie!” Claudia Kirby Heathington wrote. “Beto is a Socialist who probably has lied to you. This is a real shame you support him.”

“Wow what a let down,” Melanie Philip said. “You would pick a socialist agenda and an Anti American fellow like BETO, shame on you.”

One man was so disgusted with Nelson that he offered up his ticket to one of the legend’s upcoming shows.

“I am no longer willing to watch that hippie guitarist who supports that … socialist running for Senate,” Dakota Bell tweeted Wednesday.

Others were much more supportive of Nelson and questioned those skeptical of the country legend.

“Not sure what went wrong in your life that would make you insult Willie Nelson,” tweeted Wheeler Walker Jr., a country singer and songwriter, on Thursday. “You can argue politics all you want but you cannot argue Willie.”

In a news release announcing the concert, Nelson offered insight as to why he’s backing O’Rourke.

“My wife Annie and I have met and spoken with Beto and we share his concern for the direction things are headed,” Nelson said in the release. “Beto embodies what is special about Texas, an energy and an integrity that is completely genuine.”

The outrage comes as O’Rourke and Cruz are entangled in a tight Senate race, described by the incumbent as a “dogfight,” that has gained national spotlight in recent months.

Nelson’s political activism goes back decades, with his support of the environment, same-sex marriage and, famously, marijuana legalization. In 1980, President Jimmy Carter invited him to perform at the White House. Nelson later said that during the visit he smoked what he called a “big fat Austin torpedo” on the roof of the White House. He has supported President Barack Obama, Sen. Bernie Sanders (I-Vt.) and Hillary Clinton in recent years.

He even released a song last year inspired by President Trump, called “Delete and Fast-Forward.”

“Delete and fast-forward the news. The truth is the truth, but believe what you choose,” Nelson sings. “When we blow the whole world back to where it began, just delete and fast-forward again.”

Correction: The original version of this story incorrectly said this is the first public concert Nelson has held for a political candidate. The story and the headline have been corrected.