PHILADELPHIA (Reuters) - Democratic presidential hopeful Elizabeth Warren told a room full of liberal activists on Saturday that the party needs to fully embrace polices such as higher taxes on the wealthy, wiping out student loan debt and criminal justice reform if they want to win the White House.

The 70-year-old U.S. senator from Massachusetts said these ideas are not only supported by the activists gathered at the Netroots Nation conference in Philadelphia, the largest annual gathering of progressives in the United States, but by large majorities of the American public.

“The progressive agenda is the American agenda,” she said .

Three other Democratic candidates - former U.S. housing Secretary Julian Castro of Texas, U.S. Senator Kirsten Gillibrand of New York and Washington state Governor Jay Inslee - made similar calls for the party to embrace the progressive agenda. But it was Warren who drew the largest applause.

More than two dozen Democrats are vying to take on Republican President Donald Trump in the November 2020 election.This year, a record 3,700 people registered for Netroots Nation, organizers said, underscoring progressive enthusiasm on the eve of an election year. The conference underscored the tension between the party’s progressive base and its less vocal centrist wing - and the push from the left to have candidates choose sides.

Conference attendees said Democrats need to stop trying to peel off Trump voters by moving to the center, calling it “fool’s gold.” Instead, they need to focus on energizing its progressive base and attracting new voters.

“For any centrist to succeed, they will need to animate the people here to win. I don’t think the motivation to just beat Trump will be enough,” said Greg Robinson, 35, who works at the progressive group Living Liberally.

Inslee, 68, who has made combating climate change the centerpiece of his campaign, said the only way to implement a progressive agenda is to do away with the rule that allows one U.S. senator to block bills.

“We have to do away with the filibuster,” Inslee said.

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Castro, 44, offered several ways to combat income inequality, such as housing vouchers and enforcing the Fair Housing Act. He also said that companies such as Amazon AMZN.O unfairly pay little or no taxes and sometimes even get rebates.

“We need a tax code that rewards people who work for a living,” Castro said.

Gillibrand, 52, was asked to expand on her recent response to a white woman in Ohio who was having financial troubles due to the loss of manufacturing and who challenged the senator’s notion of white privilege.

She said she had to recognize the women’s pain because it was real.

“But what she doesn’t see as her son grows older, my son grows older, is there will be time when his whiteness protects him. ... When he walks down the street with some M&Ms wearing a hoodie, he won’t be shot.”

Warren was the only top-tier candidate to attend the annual gathering, giving her a unique opportunity to attract activists and organizers who just spent the week learning their craft. She has been a frequent speaker at the event for roughly a decade.

Warren has risen steadily in the polls in recent months, peeling voters from front-runner and former Vice President Joe Biden and progressive rival U.S. Senator Bernie Sanders of Vermont.

She repeated her calls to legalize marijuana, cancel student loan debt and tax the wealthy to help pay for things like public preschool.

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Roughly 10 of the 25 candidates running in the Democratic nominating contest were invited to speak, organizers said.

“It’s perplexing to understand why the ones who were invited didn’t come. I don’t understand the strategy. The big winner here is Warren, the only top-tier candidate to show up, and she can bask in on the glory,” said Markos Moulitsas, founder of the Daily Kos website, which chronicles progressive activism.

Moulitsas speculated that Biden’s centrist brand of politics would not play well, while U.S. Senator Kamala Harris might have been concerned about her record as a prosecutor in her home state of California.

Sanders has been challenged by the Black Lives Matter movement for not paying enough attention to criminal justice and race, Moulitsas said.

“If you can’t come into ideologically friendly territory and not stand your ground, how can we expect you to grow the kind of support they need to win the election?” Moulitsas said.