Elizabeth Warren plans to drop out of the race to be the Democrats’ presidential candidate, according to NBC News.
A source close to her campaign says she will make the announcement imminently.
It is unclear whether she will endorse either of the frontrunners, Joe Biden and Bernie Sanders.
The Massachusetts senator was hoping to be chosen as the candidate to take on Donald Trump in November’s US election.
She was seen as the most realistic prospect for a female candidate being picked to take on the Republican president – who once derided her as “Pocahontas” over her Native American ancestry.
However, a terrible Super Tuesday showing in which she failed to win any of the 14 states and came third in her home state appears to have prompted her to bow out.
Her departure comes soon after Amy Klobuchar pulled out and leaves the party with just one female candidate: Hawaii’s Tulsi Gabbard, who has collected only one delegate towards the nomination.
Billionaire Michael Bloomberg also exited the race on Wednesday – after spending a reported $500m of his own money – as the Democrat field continues to be whittled down.
Pete Buttigieg, America’s first openly gay major presidential candidate, withdrew on Monday.
Hopes for Ms Warren’s campaign were initially very high.
She drew tens of thousands to Manhattan’s Washington Square Park last summer, a scene repeated in Washington state and Minnesota.
The 70-year-old called for “structural change” to the US political system to make the economy fairer and proposed a 2% wealth tax on households worth more than $50m.
By autumn she was leading the Democrat pack, but as quickly as her status had elevated it started to fall away.
She struggled to take support from the party’s other top progressive, Bernie Sanders, with both backing policies such as government-sponsored healthcare for all and a “Green New Deal” to fight climate change.
Ms Warren also took a hit in the polls after debates in which she refused to say whether she would raise taxes on the middle class to pay for her health plan.
She tried to address the concerns by backing away from a full endorsement of Medicare for All, saying she would transition to the programme over three years.
However, that gave her rivals the ammo to label her a “flip-flopper”, and her standing with Democrat progressives was diminished.
The Massachusetts senator and Mr Sanders finally clashed directly in January when she said he had suggested privately in 2018 that a woman couldn’t win the White House.
Mr Sanders denied the claim but his rival refused to shake his hand after a debate in Iowa.
Elizabeth Warren’s departure further crystallises the Democrat race as one between Barack Obama’s former vice president, Joe Biden, and Bernie Sanders.
Mr Biden was the big winner at Super Tuesday this week, winning 10 states and capping a remarkable comeback in a campaign that seemed to be in the doldrums.
The Democrat candidate will be officially crowned at their national convention in July, with the victor taking on Donald Trump on 3 November.