US Senator Kamala Harris ended her 2020 presidential bid on Tuesday, abandoning a campaign that began with promise for a rising Democratic Party star but faltered as she struggled to raise money and make a compelling case for her candidacy.

Harris, 55, would have been the first woman and second black US president if elected next November. But her wavering views on how to solve the nation's healthcare problems and whether to embrace her past as a prosecutor were among the missteps that dragged down the campaign after its glitzy launch in January.

Her candidacy ultimately failed to resonate with African-American voters in the important early voting states of South Carolina and Nevada, and she polled poorly even in her home state of California.

Harris' abrupt departure further narrows the field of White House contenders two months before voting begins in Iowa, the first nominating contest. It underscores the difficulties of competing in a contest that once numbered more than two dozen Democratic candidates seeking the party's nod to run against Republican President Donald Trump.

“My campaign for president simply doesn't have the financial resources we need to continue,” Harris said in an email to supporters on Tuesday.

“I'm not a billionaire,” she added in a swipe at wealthy businessmen Tom Steyer and Michael Bloomberg, who are funding their own long-shot campaigns. “And as the campaign has gone on, it's become harder and harder to raise the money we need to compete.”

Harris' withdrawal marked a sharp comedown for a candidate once portrayed as “the female Obama,” a nod to the first black US president who remains hugely popular with Democratic voters.

Harris, a first-term senator for California and the state's former attorney general, was considered a top-tier contender when she launched her quest for the presidency with a rally in Oakland that drew 20,000 people.

Her political advisers, including one of California's most powerful consulting firms as well as veterans from Hillary Clinton's 2016 presidential campaign, quickly arranged national television appearances, and her questioning of Trump administration appointees in U.S. Senate hearings cemented her image as smart and tough.

Harris posted her strongest showing in the Reuters/Ipsos public opinion poll after the first Democratic debate in June, during which she briefly shifted the conversation to race relations with a sharp critique of former vice president Joe Biden's record on racial integration in the 1970s.

But Harris could not maintain the momentum and was eclipsed by rivals in fundraising.

Her support among Democrats and independents nationally slipped from 10 per cent in a June 28-July 2 poll to 2% in the latest Reuters/Ipsos poll that ran Nov. 20-22, falling from the third most popular candidate to sixth in that span.

She finished September with $9 million in cash, less than half of the nearly $26 million rival Massachusetts Senator Elizabeth Warren had on hand, according to campaign finance disclosures.

Identity problem

As Harris' campaign was plagued with internal rivalries and public complaints by former staffers that her staff was being treated poorly, the candidate herself struggled to define who she was and why she would make a good president.

“She just hasn't quite satisfactorily answered the what makes you better than the other candidates' question,'” said a longtime aide, who spoke on condition of anonymity.

Gil Duran, a former adviser who is now the opinion editor of the Sacramento Bee newspaper, said Harris was used to a California style of campaigning, where Democrats are elected fairly easily and splashy campaign events and slogans can carry the day.

“There's not really a deep bench here,” Duran said. “She can kind of stand higher than everybody else and get by on scripted politics and buzzwords. But once you are on the national stage it becomes a lot more aggressive.”

Trying to straddle the divide between Democrats' progressive and moderate wings, Harris instead failed to find her own identity, said Joel Payne, an African-American strategist who worked for Clinton in 2016.

“I think she probably ended up alienating both” camps, he said.

Payne said Harris exited the race before potentially embarrassing losses in upcoming caucuses and state nominating contests. The timing will help preserve her political future and leave open the possibility that the eventual nominee will choose her as the vice presidential candidate.

Biden did not answer when asked at a campaign event in Iowa on Tuesday if he would consider Harris as his No 2 should he become the Democratic nominee.

“She is really a solid, solid person, and loaded with talent, he told reporters. But I'm sure she's not dropping out of wanting to make the changes she cares about.”

Harris had qualified for the party's next debate on Dec 19 in Los Angeles. Other minority candidates still in the race have not yet met the polling and donor thresholds, meaning the stage could feature an all-white line-up after what was once the most diverse group of candidates in history.