CEDAR RAPIDS, Iowa (Reuters) - U.S. presidential candidate Bernie Sanders drew large, passionate crowds in Iowa this weekend, even when he was not there.

Rep. Alexandria Ocasio-Cortez speaks at a Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) campaign rally in Ames, Iowa, U.S., January 25, 2020. REUTERS/Ivan Alvarado

The U.S. Senator from Vermont has been rising in opinion polls just as Iowans prepare to pick their choice of Democratic presidential nominee on Feb. 3, but has been stuck in Washington, where he is serving as a juror in Republican President Donald Trump’s impeachment trial.

In lieu of the candidate himself, Sanders supporter Alexandria Ocasio-Cortez, a first term U.S. congresswoman from New York, has proven almost as much of a draw, filling rallies and town halls and galvanizing members of what she called a “mass movement” led by Sanders to push progressive politics.

“It doesn’t rely on any one person to carry this whole movement on their back. We all shoulder a little,” she told a group of volunteers going out to canvass for Sanders in Cedar Rapids on Saturday morning.

The strong turnout for Sanders even in his absence underscores the strength of his young and diverse base of supporters, who have rallied behind his unapologetic liberalism. But it also shows as much enthusiasm for 30-year-old Ocasio-Cortez, who became a star of U.S. left-wing politics after being elected to the House of Representatives in 2018.

Interviews with a dozen prospective caucus-goers over two days showed her backing had lent Sanders a degree of youth appeal and bolstered his progressive credentials, especially on Ocasio-Cortez’s signature issue of tackling climate change.

Sanders, proposing tax hikes for the wealthy and corporations to fund measures such as universal government-run healthcare and tuition-free college, is rising just as the first voting nears, according to a Reuters/Ipsos opinion poll this week, polling at 20% and just behind Joe Biden, the front-runner and former vice president.

In Iowa, whose first-in-the-nation caucuses have an outsized role in picking presidential nominees, Sanders is leading some polls or in a statistical tie with Biden and Pete Buttigieg, the former mayor of South Bend, Indiana.

His rise has come since Ocasio-Cortez, wildly popular among progressives and known for her bare-all social media presence, formally endorsed him in October just after a heart attack threatened to cut short his second run for president.

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“It gave him a needed boost at an important time, but also I think it signaled for a lot of young progressive people that this is the campaign that we should throw down for,” said Sayles Kasten, Iowa State director for the Sunrise Movement, a youth group organizing on climate change that endorsed Sanders this month.

Grant Woodard, an Iowa lawyer and former Democratic political operative in the state, said Ocasio-Cortez and filmmaker Michael Moore, who campaigned alongside her this week, were “cat nip” to Sanders’ base, but were not likely to expand his appeal to moderate Democrats.

Sanders, an avowed Democratic Socialist, remains a “polarizing figure in the party,” he said.

“I guess we’ll see as this plays out how much of a thirst for Democratic Socialism there in the national Democratic Party. I don’t know if it’s that great,” said Woodard.

STAR POWER

All the Democrats running for president are sending out high-profile allies, Hollywood stars and family members to campaign on their behalf or alongside them, but few attract the level of excitement seen for Ocasio-Cortez, better known by her initials AOC.

On Friday night, Sanders’ voice boomed in briefly at a college hall in Iowa City when he called in from Washington by phone after the day’s impeachment trial proceedings, but it was Ocasio-Cortez who got a rock-star welcome from the crowd of more than 800.

“She’s actually talking about issues that other politicians don’t bring up regularly, like student debt and medical care,” Max Oelmann, 19, a freshman studying social work. “I think she’s good at cutting through the bullshit, which is what a lot of people like about her.”

Ocasio-Cortez, who volunteered as an organizer for Sanders’ 2016 campaign, is the author of the Green New Deal congressional bill that Sanders incorporated into his electoral platform and which envisions massive investment in clean energy.

Her endorsement - along with the support of other high-profile progressive lawmakers Ilhan Omar and Rashida Tlaib - came at the pivotal moment of Sanders’ campaign in early October, when the 78-year-old was hospitalized and had two stents inserted in an artery.

Sanders, a Brooklyn native, vowed to stay in the race and drew nearly 26,000 people to a comeback rally alongside Ocasio-Cortez in the New York City borough of Queens, the largest crowd for any Democrat in the 2020 campaign.

‘IF SHE ENDORSES, I’M OBVIOUSLY GOING TO LIKE HIM’

During her latest swing through Iowa this weekend, Ocasio-Cortez, whose family hails from Puerto Rico, visited mainly colleges and towns with Latino populations, as Sanders’ campaign hopes to turnout both students and Hispanics – groups that tend to support his progressive platform but are historically less likely to turn out to caucus.

Sanders joined her in Iowa for more rallies after the Senate broke on Saturday.

Alli Marshall, 19, a junior at the University of Iowa who attended Friday’s rally, said she discovered Ocasio-Cortez through videos showing the congresswoman grilling witnesses in hearings. In one video that went viral on social media in October, she upbraided Facebook chief executive Mark Zuckerberg for failing to stop political misinformation on his platform.

“I was all like, wow! She’s awesome. She was just nailing them,” said Marshall, adding the congresswoman’s endorsement had helped her decide to caucus for Sanders and volunteer for his campaign.

“Honestly, if she was a candidate, I would vote for her, but she’s not. So if she endorses (Sanders), I’m obviously going to like him.”