“Our government’s supposed to work for all of us, but instead, it has become a tool for the wealthy and well-connected,” Warren said.

In a video released online , Warren, 69, offered a broad rebuke of Republicans from Ronald Reagan to Trump, painting a picture of a nation controlled by a small class of billionaires and corporate interests who have bought and paid for lax regulation in Washington. She cast herself as the champion who will change that.

WASHINGTON — Elizabeth Warren, the Massachusetts senator who has built an outsize profile as an economic populist and a progressive foil to President Trump, formally announced on Monday that she is exploring a run for the presidency in 2020.


“We can make our economy work for all of us. We can rebuild America’s middle class, but this time, we’ve got to build it for everyone,” Warren said, explaining that she is launching an exploratory committee, which will allow her to raise money for a likely presidential campaign but does not officially make her a candidate.

Although she enters the campaign after a rocky autumn, Warren is the best-known political figure so far to officially test out what is expected to be the most crowded Democratic presidential field in a generation. Her announcement signals the start of a boisterous primary, in which numerous serious candidates will likely jostle for the attention of voters in a party that is united by frustration with the president but deeply divided over how to beat him in 2020.

Warren’s answer, as laid out in her announcement video, is with a laser focus on themes of unfairness and economic inequality in America. Those same themes helped fuel her rapid rise from being a respected academic with an expertise in bankruptcy law to a titan of the liberal left and one of the top fund-raisers in the Senate. In the video, Warren also emphasized the role of race, saying that, while things have gotten tougher for all working families, minorities face a “steeper and rockier” path because of discrimination.


“America’s middle class is under attack,” she said, forcefully. “Billionaires and big corporations decided they wanted more of the pie, and they enlisted politicians to cut ’em a fatter slice.”

At a press conference held at her home in Cambridge, Warren declared: “I’m in the fight for all our families.”

The timing of Warren’s announcement — on New Year’s Eve — was intended to allow her to hire staff and build her campaign apparatus. She will ramp up her operation right away, with travel to early primary states expected soon, according to a source close to the campaign.

Perhaps more than anyone else in the potential field, Warren has cast herself as a fighter, scrapping with Trump directly in public speeches and on Twitter, where she has called him a “money grubber” and urged the Cabinet to remove him from office using the 25th Amendment. For his part, Trump has shown a fixation with Warren above and beyond the rest of the potential 2020 Democrats. Asked by Fox News Monday if Warren really thinks she could beat him, the president said, “You’d have to ask her psychiatrist.”

Trump’s frequent taunts about her claims to Native American heritage led Warren to release the results of a DNA test in October showing evidence of distant ancestry.


That move unsettled some progressives and created questions about her political instincts as she takes a major step onto the national stage. She appears to have slipped in the polls in recent months, although the significance of polls two years ahead of the general election is not clear. And her willingness to get into the ring with Trump, while appealing to voters who are seeking a political fighter, may turn off those looking for a Barack Obama-style candidate with a more positive message.

“The ability to challenge Donald Trump, to take him on and show you’re not scared or intimidated by his bullying is something that everybody who runs for the Democratic nomination is going to need to demonstrate,” said Anita Dunn, a former Obama adviser. “The question is, who is seen as doing it effectively?”

Liberals responded positively to the end-of-year announcement. On Twitter, Symone D. Sanders, the former press secretary for Senator Bernie Sanders, and the podcast host Jon Favreau quickly praised the clarity and authenticity of Warren’s messaging in the video. Meanwhile, Ronna McDaniel, the chair of the Republican National Committee, called Warren an “extreme far-left obstructionist,” underscoring the fact that her tangles with the GOP have already made her a well-established subject of Republicans’ ire.

Democratic strategists said Warren has the potential to mount a strong campaign by drawing upon her formidable list of small-dollar donors, impressive online following, and a network that spans all 50 states. Her fund-raising prowess alone is enough to put her in the top tier of potential candidates.


And her long association with such issues as consumer finance, inequality, and corporate largesse gives her brand of populism a significant credibility boost, which could help her connect with voters who are seeking authenticity.

“You always know where Elizabeth Warren stands, and you can’t say that about many elected officials or politicians,” said Mary Anne Marsh, a Democratic strategist in Boston.

But as the field takes shape, the former Harvard law professor is likely to come up against numerous candidates beating the same drums of economic fairness. It is a marked departure from 2016, when left-leaning grass-roots groups were hungry for Warren to take on the more establishment Hillary Clinton in the primary as their candidate.

Her focus on reining in Wall Street and corporate greed dovetails significantly with Bernie Sanders’ message, a problem for her if the 77-year-old senator from Vermont with a huge progressive following should decide to get into the race.

Warren has been working hard to make inroads with black voters, but she will likely face dynamic candidates of color such as Senator Cory Booker of New Jersey and Senator Kamala Harris of California, who may appeal to voters seeking a standard-bearer who represents the party’s diversity.

And while she could draw in women voters who have seized on the “Nevertheless, she persisted,” slogan that arose after Senate majority leader Mitch McConnell used an obscure rule to silence Warren during a 2017 speech in the Senate, she will likely have to compete with numerous other female candidates for their attention.


Meanwhile, outgoing Representative Beto O’Rourke, 46, of Texas has shot up in recent polls of early primary states, suggesting Democrats may want a newcomer with an uplifting style to be their nominee.

“Every candidate is going to have the challenge of how you break through,” said Doug Rubin, a Massachusetts-based strategist who worked on Warren’s 2012 initial Senate campaign.

Democratic voters, wary after a bruising defeat to Trump, are also likely to closely vet Warren’s chances in a general election, when she would need to appeal to independent voters as well as Democrats.

“I really think in Senator Warren’s case, the biggest challenge she faces is the question of electability,” said Jerry Crawford, a prominent Iowa Democrat.

No issue raises that question more than the controversy over Warren’s ancestry claims, which went unaddressed in the video. She has said having Native American blood was part of her family lore, and she identified herself as such during part of her academic career. She has released extensive documentation to prove her claims did not help her get hired at Harvard, and then in October made public a DNA test showing she likely had a distant indigenous ancestor. But Republicans seized on the tiny percentage of indigenous ancestry found to suggest her claims were still dubious, while progressives and some Native American groups were unsettled by her use of genetics to prove a claim about her ethnicity.

Some on the left charged she had let Trump get into her head, which may be why she does not say his name in the video and his image does not appear until 2.5 minutes in.

Warren, who grew up in Oklahoma and still speaks with a slight twang, will likely draw on her background to help her connect with economically struggling voters. Her video features photographs from her modest upbringing and early years of her career. She connects her populist economic message to her past, often talking about her childhood growing up on the “ragged edge of the middle class,” when her mother was able to make ends meet by getting a minimum wage job at Sears after Warren’s father had a heart attack.

“She comes from a working-class background — I can identify with that,” said LaTosha Brown, a cofounder of the Atlanta-based Black Voters Matter fund, earlier this month.

Warren took a winding path into academia, dropping out of her first university but eventually becoming a bankruptcy law expert and a Harvard professor. She broke into politics after then-President Obama took a shine to her idea for a federal consumer financial protection bureau that would crack down on deceptive practices of lenders. Her bureau became law when Democrats passed the Dodd-Frank financial reform act in 2010, but she was stymied from leading it by Republican opposition. Warren ran for Senate instead, defeating Republican incumbent Scott Brown in 2012. She was reelected in November.

“I never thought I was going to be in public office — my whole life I never thought that,” Warren told the Globe earlier this year. “I was going to be a public school teacher and then I became a professor. Pretty amazing for the daughter of a janitor.”

Jess Bidgood can be reached at Jess.Bidgood@globe.com. Liz Goodwin can be reached at elizabeth.goodwin@globe.com.