The thousands of people who turned up to Austin's Auditorium Shores for the Beto O'Rourke rally on Saturday night (Sept. 29) were expecting to hear Willie Nelson sing through some of his greatest hits -- but the brand new song written for that specific occasion was certainly an encouraging surprise.

The outlaw country icon wrapped his brief headlining set with a pointed anthem, "Vote 'Em Out," that had attendees belting out the chorus on the walk back over the river long after he left the stage. O'Rourke is the Democratic candidate hoping to oust Ted Cruz from his senate seat, and Nelson made his loyalties plain with a cheeky tune perfect for a grand finale sing-along.

The song's "Vote 'em out!" refrain is certainly straightforward, but Nelson worked some motivational wordplay into each verse while stressing how important it was to exercise the right to vote in order to drive this "bunch of clowns you voted in" out of office. (A sample line: "The biggest gun we got/Is called the ballot box/If you don't like who's in there, vote 'em out.")

O'Rourke -- who delivered a rousing speech that touched on family separation at the border, climate change, the prison industrial complex, police brutality, universal healthcare, discrimination against the LBGTQ community and other issues concerning Texan voters before Nelson walked up to the mic -- watched the majority of Nelson's set from the back of the small stage, but joined him to sing a few lines of "On the Road Again." 

In addition to Nelson and his band, the bill for the evening was chock full of Texan talent, with Leon Bridges, Tameca Jones, Carrie Rodriguez and Joe Ely all throwing their support behind O'Rourke's campaign.

Watch Willie Nelson sing a few bars of "Vote 'Em Out" and listen to the studio version, which debuted on Oct. 11, below.