Willie Nelson took to the stage in Austin on Saturday night wearing a “Beto for Texas” cap over his trademark braided hair. It didn’t last long – within minutes he had flung the hat into the crowd and replaced it with his trusted red bandana.

That Nelson was there in the heart of the capital to lend the power of his legend to Beto O’Rourke, the Democrat who is roiling the state with an insurgent attempt to unseat Ted Cruz from his US Senate seat, remained beyond doubt. He made no effort to remove his Beto T-shirt.

But he let his music do the talking. Literally, in the case of a new song that he gave its debut which left little to the imagination.

If you don’t like who’s in there, vote ‘em out That’s what election day is all about When they are gone, we will sing and shout

Nelson has been the unofficial figurehead of Texas since his return from Nashville to Austin in 1972. With lyrics that address the daily struggles of cowboys, farmers and lovers, he has managed to achieve the impossible: attracting the adoration of Texans across generations, spanning city and countryside and bridging the ever-widening political divide.

Who else can bring hippies, hipsters and Trump supporters under one roof?

This time, though, it was too much for many Cruz-supporting Texans. Previously diehard Willie fans erupted in anger after the Austin rally was announced, griping that his decision to appear for O’Rourke – Nelson’s first public performance for a political candidate – was beyond the pale.

But at 85, that didn’t seem to bother Willie. Besides, his new-found detractors should have known that his embrace of progressive and liberal politics is decades old, stretching back to the famous time he got high on the roof of Jimmy Carter’s White House.

It’s the music that brings us all together. It’s real. It’s for each one of us John Dromgoole

The pre-rally hoo-ha appeared to faze Nelson not one bit. He came on stage with his arms around a visibly sweaty O’Rourke, who had just promised universal healthcare and immigration reform to an appreciative 30,000-strong crowd. The Democratic candidate, a US representative from El Paso, had also pledged legalization of marijuana – a favorite of Nelson’s, who has his own cannabis company selling in states in which the drug is already permitted.

The last time they appeared together, at Willie’s annual Fourth of July picnic, O’Rourke reprised his punk rocker past and played guitar during It’s All Going to Pot and Will the Circle Be Unbroken. This time he just sang along with the chorus, standing slightly to one side and looking a little awkward.

At least the song he came on for had a resonance for both men: On the Road Again. Nelson still spends most of his life performing with the Family, sustaining a grueling rate of about 150 gigs a year and returning rarely to his spiritual home in Austin.

That relentless record is capped only by O’Rourke’s, who framed his unlikely charge on Cruz’s seat with a year-long tour to every county in Texas: all 254 of them.

Among the largely young and politically fired-up crowd, there were some serious Willie Nelson acolytes. John Dromgoole, 71, aka the Natural Gardener, has been following the musician since his early Austin days at the Armadillo World Headquarters in the Seventies.

John Dromgoole, 71, has been following the musician since his early Austin days at the Armadillo World Headquarters in the Seventies. Photograph: Ed Pilkington/The Guardian

Dromgoole, who now runs a garden nursery, is friends with Nelson’s second wife (of four), Connie. One of the areas at his nursery is set aside as a quiet homage to Willie, featuring a replica in stone and vegetation of the star’s famous guitar, Trigger.

“It’s the music that brings us all together,” Dromgoole said, his hair braided in a mirror image of Nelson’s. “It’s real. It’s for each one of us – when you hear his songs each one of us hears that it is being sung only for us. That’s his art.”

Lane Mann, 25, was also in the crowd wearing an On the Road T-shirt. It’s an original, from the 1980s, and she was wearing it in honor of her grandfather Mike, a huge Willie fan who died this year.

Lane’s mother, Jules Mann, 59, was wearing a customized T-shirt that said: “Willie is My Spiritual Animal”. Mother and daughter sat side by side, but carried a slightly different perspective.

Lane Mann was there she said fifty-fifty: she loved Willie but really wanted to hear O’Rourke and to be uplifted by the hope of his politics. “He’s uniting us, travelling all over Texas and showing progressive people that they are not alone.”

Her mother was all-in for Willie: “He’s about the freedom of the open road, not giving a damn, and he writes sweet lyrics along the way.”