Sen. Elizabeth Warren (Mass.) became the highest-profile Democrat to officially test the waters for a 2020 presidential run, with the launch of an exploratory committee that allows her to start raising money for a campaign.

Warren is making the announcement Monday morning in an email to supporters, accompanied by a video laying out the case for her candidacy. It hews to her core message, that the system is no longer helping working-class Americans.

From her email:

The problem isn’t caused by some indisputable law of physics, like gravity. The problem isn’t that people aren’t willing to work hard. The problem starts in Washington. Our government has been bought and paid for by a bunch of billionaires and giant corporations that think they get to dictate the rules that affect everyone. Tax loopholes. Prescription drug pricing. Financial rules. Environmental protection. These companies define policies that are great for their bottom line, while good, honest people who work hard get squeezed harder every year. It’s corruption, pure and simple. That’s not how government is supposed to work. You know it. I know it. And we know it is time to fight back. I’m forever grateful that I got a chance to go to college for $50 a semester, a chance that opened a million doors for me. I’m grateful, and I’m determined. That’s why I fight my heart out so that everyone gets a real chance in life, a chance to build something solid, a chance to create their piece of the American dream.

While Warren is not yet a formal candidate, it is unprecedented in recent political history for a high-profile candidate to decide not to run for president after launching an exploratory committee.

Warren will be on Capitol Hill for the first day of the new 116th Congress on Thursday, and an aide said she expects to hit the road soon for visits to the early primary states.

Warren is one of the fiercest defenders of Dodd-Frank, a massive financial reform bill signed by President Barack Obama in 2010. That law created the Consumer Financial Protection Bureau, which Warren first proposed in 2007 as a Harvard Law School professor.

Long before her time in the Senate, Warren attracted the ire of Republicans. While still a professor, she promised, in an interview with HuffPost, to use her position to fight for a strong Dodd-Frank and CFPB, pledging to put “plenty of blood and teeth” on the Senate floor to do so.

Warren wanted to become director of the CFPB, but GOP senators were so opposed to her appointment that Obama never even nominated her, convinced she couldn’t be confirmed. Instead, she ran for Senate in 2012, taking a seat away from Republicans ― the seat had been won by Scott Brown in a special election ― and becoming a colleague of those same senators who had criticized her.

“We created America’s first consumer watchdog to hold the big banks accountable,” Warren says in her announcement video. “I never thought I’d run for office. Not in a million years. But when Republican senators tried to sabotage the reforms and run me out of town, I went back to Massachusetts and ran against one of them. And I beat him.”

In the Senate, Warren has gained national attention in Senate Banking Committee hearings for going after bank executives and government officials who are supposed to be overseeing them. Unlike some senators in some hearings, Warren understands financial policy just as well, if not better, than the people she questions. After Wells Fargo was caught opening millions of fake bank and credit card accounts without customers’ consent, Warren tore into the CEO, John Stumpf.

“Your definition of accountability is to push this on your low-level employees,” she said. “This is gutless leadership.”

She also, like many other high-profile female politicians, has a way of getting under the skin of some of her male colleagues. Republican senators tried to silence Warren during a speech against Jeff Sessions’ nomination for attorney general in 2017, with Senate Majority Leader Mitch McConnell (R-Ky.) explaining, “Sen. Warren was giving a lengthy speech. She had appeared to violate the rule. She was warned. She was given an explanation. Nevertheless, she persisted.”

Chris J Ratcliffe via Getty Images

That last line became a rallying cry for feminists, with Warren at the front and center of the controversy.

She also became one of the most high-profile critics of President Donald Trump, and he took to calling her “Pocahontas” to mock her for claiming Native American ancestry. In October, Warren released a DNA test showing “strong evidence” that she had a Native American ancestor in her family tree, accompanied by a video talking about her family story.

The DNA test did nothing to silence her critics, and the rollout raised questions, even among Democrats, about whether she understands minority issues fully enough, and whether she’s truly the strongest person to go up against Trump.

Launching an exploratory committee early allows the candidate to start raising money as soon as possible. Warren already has several dozen staffers in primary and other battleground states, whom she sent there during the midterms to help elect other Democrats. Many of them have stayed, however, and the exploratory committee will allow her to raise the funds to keep paying them.

Without ever running for president, Warren has become one of the most prolific small-dollar fundraisers in the history of Democratic politics. She raised $42 million, nearly half of that in contributions under $200, in her 2012 run to defeat Brown. And she raised $30 million over the past six years, with two-thirds of that haul coming from small dollar donors. She’s expected to rely on a similar strategy to fund her presidential bid, and like most Democratic candidates in 2020, isn’t expected to rely on a super PAC to boost her candidacy during the primary.

So far, the only Democrat officially running in 2020 is Rep. John Delaney (Md.). Julián Castro, Obama’s former secretary of Housing and Urban Development, has already launched an exploratory committee and plans to announce his next steps in San Antonio, Texas, on Jan. 12. Other potential contenders, like Sens. Kamala Harris (Calif.), Cory Booker (N.J.) and Kirsten Gillibrand (N.Y.) are also expected to potentially jump into the race in the coming weeks.

While Vermont Sen. Bernie Sanders laid exclusive claim to the progressive lane in his 2016 primary challenge to former Secretary of State Hillary Clinton, Warren will likely face stiff competition to win over progressive voters, including from Sanders himself. (The two senators, longtime political allies, met earlier this month to discuss the likelihood both would run for president.) Warren has tried to separate herself from Sanders by noting she doesn’t share his socialist beliefs.

Other progressives who could enter the presidential contest include Harris, Oregon Sen. Jeff Merkley, Ohio Sen. Sherrod Brown and billionaire and major Democratic donor Tom Steyer.