Dozens of people weighed in on Willie's Facebook page Wednesday after he shared a story about the upcoming rally in Austin.
While some people told Willie he needs to stay out of politics, others threw insults at the music legend. Still, some others applauded Willie's contribution to the 2018 campaign.
The event is set for September 29 at Austin's Auditorium Shores.
Nelson is scheduled to perform alongside Joe Ely, Carrie Rodriguez, Tameca Jones and Nelson's sons, Lukas and Micah Nelson.
If you're interested in seeing the show, tickets are free -- but an RSVP is required.
O'Rourke is hoping to unseat incumbent Republican Sen. Ted Cruz in November's election.
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