US Senator Elizabeth Warren has formally launched her bid to stand for the White House in 2020 with a speech in which she promised to tackle economic inequality.
She is the latest Democrat to launch a campaign to become the party's presidential candidate.
Even before she had taken to the stage, President Donald Trump's 2020 campaign team had responded calling her a fraud.
It is the first such intervention to target a possible Trump contender.
"The American people will reject her dishonest campaign and socialist ideas like the Green New Deal, that will raise taxes, kill jobs and crush America's middle-class," Mr Trump's campaign manager Brad Pascale wrote.
He also accused her of "impersonating and disrespecting" Native Americans "to advance her professional career," referring to a DNA test she took to prove her Cherokee ancestry. Mr Trump had long been calling her "fake Pocahontas".
Ms Warren has apologised for taking the test.
In her speech on Saturday in Lawrence, in her home state of Massachusetts, Ms Warren called Mr Trump "the latest and most extreme symptom of what's gone wrong in America, a product of a rigged system that props up the rich and powerful and kicks dirt on everyone else".
She added: "This is the fight of our lives, the fight to build an America where dreams are possible, an America that works for everyone."
A star in the progressive left
In the shadow of long-unused smoke stacks, at the site of a famous factory strike more than a century ago, Elizabeth Warren formally launched her presidential bid.
She used the backdrop to highlight what she sees as the plight of an American working class that has been left behind by rapacious big business and indifferent government.
Despite sub-zero temperatures and a blustery wind, an estimated crowd of several thousand turned out to hear the Massachusetts senator pledge to fight corruption in Washington, level the economic playing field and reform the US democratic process.
Warren enters a crowded presidential field, as Democrats tell pollsters they want to find the candidate most able to beat Donald Trump.
There were some in Ms Warren's campaign kick-off crowd who expressed concern that her struggles to explain her past claims of Native American heritage could make her vulnerable to attack.
Ms Warren has long been a star in the progressive left, however, and she has already built a formidable nationwide campaign. She has just under a year to make her case, before voters start rendering their judgement.