Country music icon Willie Nelson debuted a surprise political anthem during a rally for Texas Rep. Beto O’Rourke, the state's Democratic Senate nominee.

Nelson, who performed at O’Rourke's rally on Saturday night in Austin, finished his headlining set with a premiere of “Vote ‘Em Out,” a rallying cry to get voters to the polls.

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"The biggest gun we got is called the ballot box,” Nelson sang. “If you don't like who's in there, vote 'em out.”

“Election Day is coming ‘round again,” Nelson sang, urging attendees to cast their ballots to vote out this "bunch of clowns you voted in." The audience enthusiastically sang along with Nelson during the performance.

The country rock star has made political statements before, with a Trump-inspired song “Delete and Fast-Forward” released last year.

Nelson faced backlash from many fans for headlining a rally for O’Rourke, who is running to defeat Sen. Ted CruzRafael (Ted) Edward CruzCongress can stop the war on science O'Rourke blogs from road trip: 'Have been stuck lately. In and out of a funk' Texas governor, top lawmakers tell Trump not to use hurricane relief funds to build border wall MORE (R-Texas), but said earlier this month that he doesn’t care.

Polls have repeatedly shown a tight race between Cruz and O’Rourke in the red state, which has not elected a Democrat to the Senate in decades.