It was billed as a rally for Bernie Sanders’ presidential campaign. But the only aging white man on the platform was the film-maker Michael Moore, and attendee Brittany Springmeier wasn’t there to see him.

She was in Iowa City for real star of the show, Alexandria Ocasio-Cortez.

“She’s speaking for us. She’s speaking for the people. She has a passion for the millennials. She’s speaking for everyone in America who doesn’t have a voice,” said Springmeier, a millennial herself who is unable to work because of a disability.

With the Vermont senator trapped in Washington DC by the impeachment hearings, Ocasio-Cortez was fronting for him at the University of Iowa on Friday evening in the last days before the Iowa Democratic caucuses.

Much of the crowd had already made up its mind to back Sanders, which was just as well because the New York congresswoman gave a 26-minute speech without once mentioning the man she was ostensibly there to promote. A passionate discourse on healthcare and the case for comprehensive public insurance, a cause at the heart of Sanders campaign, then gave way to a rousing appeal to build a movement to transform “a nation in decline”.

Ocasio-Cortez disparaged the Democratic leadership in Congress as fearful of any radical policies that might cost votes and called on supporters to “come together and organise” to repeated cheers.

But through it all, even as Sanders picture stared down on her, his name did not once cross the congresswoman’s lips.

Supporters of Bernie Sanders Friday Iowa City, Iowa. Photograph: Sue Ogrocki/AP

Ocasio-Cortez has been unstinting in her support of Sanders’ presidential bid but Friday’s rally will only reinforce the perception that his campaign also provides her with a platform to push a more visionary agenda. That in turn has fueled media speculation about the extent of the 30 year-old’s ambitions, and the possibility she might run for the White House herself in 2024 – should Trump win a second term.

Whatever her plans, the congresswoman will not have been discouraged by the reception in Iowa City, where she was greeted with an enthusiasm bordering on adulation.

Jonathan Katz, a high school math teacher from New York City who travelled to Iowa to canvass for Sanders, was at the rally specifically to see Ocasio-Cortez.

“When she showed the courage after Bernie’s heart attack to say ‘I’m going to be supporting Bernie’, my respect went up 1,000%. Because here’s someone at Bernie’s most difficult moment in the campaign saying ‘I’m with you Bernie’,” said Katz.

Ocasio-Cortez’s backing has meant more than throwing her weight behind Sanders’ positions. She has amplified some of them, not least on the environment with her push for a Green New Deal, and injected a much greater diversity of voices into the Vermont senator’s campaign, which he has frankly admitted were lacking in his 2016 run.

“She’s been very important to Bernie, bringing people in, especially young people,” said Springmeier. “She’s helped bring in minorities, bring some light to the fact that they don’t really have a voice. I think a lot of people are drawn to her who may not otherwise have been interested in politics, and that helps Bernie.

“I really hope she continues on the politics. She’s a force to be reckoned with. I really think she’s going to do great things for the people, for we the people. She’s working in the establishment but I think she’s going to be speaking for us.”

Alexandria Ocasio-Cortez takes part in a march following antisemitic attacks in New York City. Photograph: John Lamparski/Echoes Wire/Barcroft Media

If Ocasio-Cortez has reinforced the Sanders campaign, it’s clear she can also draw from that enhanced strength. For some of Sanders supporters, she offers a vision beyond his presidential campaign.

Wendy Stevenson, a librarian who caucused for Sanders four years ago, came to the rally with her 11-year-old daughter, Estelle, who wanted to see Ocasio-Cortez after watching a Netflix documentary about her.

“I love her vision. I love her guts to go in first term as a representative and propose the Green New Deal. It changes the way our economy will work. It’s exciting. You need that kind of energy and ideas out there. And she’s not scared to challenge the establishment. Even the Democrats, she’s pushing them further than they feel comfortable going. I love having that voice,” she said.

But for all that, Stevenson is not sure on where Ocasio-Cortez should set her sights. For now she wants to see her remain in Congress, where she thinks she could rise to great heights and have real power and influence over the policies that matter most.

“I hope she’ll be a powerful future politician that can change the way things are done. I feel like she really feels strongly about representing her people in her district. She’s still young. I’m excited that things are moving further to the left with a lot more fresh ideas. I really hope she is the future.”