Country music icon Willie Nelson's decades of progressive political activism appeared to have gone unnoticed by many of his right-wing fans, with outrage erupting this week over the musician's plans to perform at a rally for Democratic candidate for U.S. Senate Beto O'Rourke.

Nelson shared with his fans Wednesday that he counts himself among O'Rourke's supporters in a press release.

"My wife Annie and I have met and spoken with Beto and we share his concern for the direction things are headed," the singer and songwriter wrote. "Beto embodies what is special about Texas, an energy and an integrity that is completely genuine."

The statement noted that Nelson's appearance at a free show in Austin on September 29 will be his first in support of a specific candidate for public office, but it came as no surprise to those who have followed Nelson's involvement in anti-war efforts, Farm Aid, marijuana legalization, LGBTQ rights, and his campaign in favor of biofuels as an alternative to fossil fuels.

O'Rourke has been campaigning for months to unseat Sen. Ted Cruz (R-Texas), on a platform promoting an end to the militarization of immigration enforcement, decriminalization of marijuana, achieving universal healthcare, strengthening gun control laws, and other progressive initiatives.

Some conservative fans expressed outrage at Nelson's endorsement of the candidate, with many saying they would boycott his music and concerts.

"You should stay out of politics," wrote one on his Facebook page. "I'm a lifelong fan, this is not a smart move."

"Goodbye Willie...You would pick a socialist agenda and an Anti-American fellow like Beto, shame on you," added another.

"I haven't been this disappointed since the day I used my 'Dixie Chicks' CDs for target practice," another posted.

The outcry provoked led fans to come to Nelson's defense—reminding his detractors of his widely-known legacy and celebrating his most recent championing of progressive values.