“If people are going to run for president, it shouldn’t be about reaching in their pockets and trying to drown out everybody’s voice with tens of millions of dollars,” she said.
“It should be about getting out and talking to voters, and asking them to volunteer, because they believe in what you’re fighting for.”
She added: “That is the only way we’re going to repair this democracy in America.”
Up until this point in the race to become the Democratic Party’s presidential nominee, the Massachusetts senator has largely avoided criticism of other candidates. Indeed, such has been her determination to focus on matters of policy, that she has even been criticised by some pundits for declining to attack her rivals.
But after Mr Bloomberg, the former mayor of New York, finally confirmed over the weekend that he was entering the race and would be spending $37m (£29m) of his own money on television adverts, she levelled several blows as she campaigned in Iowa, the first state to hold its Democratic primary ballot, and where she has recently seen her frontrunner status taken away by Pete Buttigieg.
Speaking to potential voters in Ankeny, nine miles north of the state capital, Des Moines, Ms Warren opened her remarks by focusing on Mr Bloomberg, who has said his campaign will not seek donations.
“Michael Bloomberg is making a bet about democracy in 2020. He doesn’t need people, he only needs bags and bags of money. I think Michael Bloomberg is wrong,” she said.
“If Michael Bloomberg’s version of democracy wins, then democracy changes.”
On Monday evening, Ms Warren appeared before a packed crowd at the Val Air Ballroom, a venue that dates to 1939 and the entrance of which carries signed black-and-white photographs from acts such as The Belmonts and Count Basie. A more recent one, of country singer Lucinda Williams, is in colour.
Ms Warren, 70, launched into what has become a warm, emotive stump speech, telling the story of her mother, who donned her only proper dress and enrolled in a minimum-wage job at a Sears department store, rather than lose the family home.
Things had changed since then, she said: today, no single mother can raise a child on the minimum wage. The middle class has been hollowed out, she said, and it is tougher than ever for people to get an economic toehold, especially for people of colour.
Ms Warren set out the three-pronged plan she would oversee if elected: fighting corruption in its various forms, restructuring the economy and preserving the nation’s democracy. She said she had detailed and costed plans to provide tuition-free college, universal healthcare and massive investment in education, by ensuring large corporations paid more in taxes, and by asking the most well-off to contribute more.
She said her plans had been criticised by some of the country’s very wealthiest, and joked about some of them going on television and shedding tears, an apparent reference to former Goldman Sachs executive Leon Cooperman, who condemned her proposals to place an annual 2 per cent tax on every dollar that a household has above $50m.
In what may have been another jab at Mr Bloomberg, she said that some of the critical billionaires had urged their friends to get in the presidential race. “I guess they figure it’s cheaper to spend $100m on this than the 2 per cent.”
Mr Bloomberg’s campaign has yet to comment on Ms Warren’s remarks, but at his first campaign event on Monday in Norfolk, Virginia, he defended using his wealth to underwrite his candidacy.
“For years I’ve been using my resources for the things that matter to me,” he said, according to a video posted by PBS. “I am going to make my case and let the voters who are plenty smart make their choice.”
Ms Warren received long, loud applause, and the line for selfies with the former law professor snaked all the way down the ballroom to the door.
“I thought it was great,” said Nicole Gustanson, 28, as she left the event. “I like her specifics about things. I will volunteer for her.”
But Ms Warren is not the only Democrat with lots of enthusiastic supporters in Iowa. Having overtaken rivals Joe Biden and Bernie Sanders in this crucial marker in the race for the White House, she has since watched as Mr Buttigieg’s numbers have soared here in a succession of polls.
An average of those, collated by RealClearPolitics, gives the mayor of South Bend, Indiana, a six-point advantage over Ms Warren at this point, scoring them 24-18.
Indeed, there were plenty of people present on Monday night who appeared to be trying to decide between Ms Warren and Mr Buttigieg. Raul Canahui, 29, an architect, said he liked the fact that Mr Buttigieg had his roots in the working, or middle class, of the Midwest. He added: “Joe Biden has a lot of experience, but he has made some bad statements in recent months, so I am not sure about him.”
Speaking to the media after the event in Des Moines, Ms Warren was not asked about Mr Buttigieg. A number of her supporters have pointed out that while Mr Buttigieg is leading the pack in Iowa, he is doing far less well in states where there is a larger number of people of colour, including South Carolina.
RealClearPolitics’s national average puts Mr Biden on 29 points, Mr Sanders on 19 and Ms Warren on 18.
Ms Warren finished her speech to voters with a veiled reference to recent remarks by former president Barack Obama, who suggested most Americans favoured positive change, but not a revolution.
“We need big ideas and we need to fight for it,” she said. “I get it. You can sound smug with these big ideas. But if you give up on them, what happens to the people whose lives would have been improved by those ideas?”
She added: “I believe 2020 is our time.”
Additional reporting by Reuters
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