Senator Elizabeth Warren (D-Mass) worked for years to build relationships with black leaders, an effort that included becoming one of the first white politicians to endorse the Black Lives Matter movement. But when she got in trouble recently for releasing a DNA test that struck many as racially insensitive, few black leaders rushed to her defence.

The episode suggests a lack of depth in the alliances she has forged among non-white activists and influencers, a group she must lean on to vouch for her should she go ahead with a presidential bid.

It is difficult to see a path to nomination without some support from black voters. More than 8 in 10 African Americans identify with or lean towards the Democratic Party, and on average, 25 per cent of the primary voters and caucus-goers in the last presidential contest were black. In 2016, African American voters made up 62 per cent of the electorate in South Carolina, a key early-voting state. They also make up a large share of the vote in southern states that cast ballots on Super Tuesday or later in the calendar.

In 2016, black voters were essential to Hillary Clinton's nomination, with 78 per cent siding with her over Senator Bernie Sanders (I-Vt) (in primaries and caucuses where exit polls were available). That task will be far more difficult for Ms Warren and any other white Democratic candidates in 2020 because of the potential presence of at least two black senators, Kamala D Harris of California and Cory Booker of New Jersey.

Ms Warren has been travelling the country to speak in front of black audiences, added black staffers in key roles, and cultivating key black leaders. But there remains an awkwardness she has not quite addressed, according to strategists who focus on the demographic.

The reasons include her message of economic populism that can clang in the community, her ties to Boston and her DNA test, which dredged up ugly reminders about defining ethnicity.

"African Americans are a strong constituency in the Democratic Party, in fact the most loyal voting bloc in the party, and she is not so well-known or connected - that I know of," said Antjuan Seawright, a South Carolina-based Democratic operative who advised Ms Clinton's 2016 campaign in the state.

"We want to feel appreciated. We want to feel courted," he said, noting he has heard from a number of potential Democratic candidates, but not from Ms Warren. "You can't come in as a fly-by-night candidate and expect to garner support just because you show up."

The economic populist agenda Ms Warren champions does not always connect with black communities because it can be seen as de-emphasising racism as a root problem for inequality, black leaders say, even though Ms Warren has gone out of her way to underscore the impact of racism among communities of colour.

Adding to this disconnect is Ms Warren's geographic base. Her home state of Massachusetts is largely white; its capital and the probable area for Ms Warren's campaign headquarters is Boston, a city whose long history of racial strife makes it shorthand for racism among many blacks.

As one Democratic congressional staffer put it, the city of Boston is seen as "the Mississippi of the north".

Another difficulty stems from Ms Warren's fraught relationship with her racial identity. As a politician, she has stumbled over a claim made during parts of her earlier teaching career that she was a Native American.

In response to gibes from President Trump, who belittled her as "Pocahontas", she recently released a DNA test that showed she may have a distant Native American relative. Minority groups responded by criticising Ms Warren as seeking to define ethnic identity by a blood test.

Few black leaders defended Ms Warren after she made the test public in October. Although, former interim Democratic National Committee chairwoman Donna Brazile tried to pivot away when asked about it: "You want to know what's in her DNA?" she said on MSNBC. "A willingness to fight for our democracy."

Others have been far blunter.

"She would have done much better not to address Trump's racism," said Aimee Allison, the executive director of She the People, a group that supports non-white female candidates.

Ms Allison's group released a straw poll of black female activists and strategists earlier in December that illustrated how much work Ms Warren has ahead of her among those influential leaders. Just 22 per cent picked Ms Warren as one of their top three candidates.

Among those who finished ahead of Ms Warren were potential black candidates Ms Harris and Mr Booker. But Ms Warren was also behind two possible contenders who are white: One was Texas Representative Beto O'Rourke, who during his unsuccessful US Senate campaign offered a full-throated and later viral defence of NFL players who take a knee during the national anthem. The second was Joe Biden, vice president to the nation's first black commander-in-chief.

Who could be running against Trump in 2020? Show all 23 1 /23 Who could be running against Trump in 2020? Who could be running against Trump in 2020? Joe Biden The former vice president - poised to be a frontrunner - has announced his run. He recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well AFP/Getty Who could be running against Trump in 2020? Bernie Sanders The 2016 runner-up has announced that he will be running again in 2020 Getty Who could be running against Trump in 2020? Hillary Clinton The 2016 Democratic presidential candidate and former Secretary of State says she is “still considering” whether she will run again. Getty Who could be running against Trump in 2020? Pete Buttigieg The Indiana mayor and war veteran will be running for president. If elected, he would be the first openly LGBT+ president in American history. Getty Who could be running against Trump in 2020? Kamala Harris The former California attorney general will be running for president in 2020. Introduced to the national stage during Jeff Sessions’ testimony, she has endorsed Medicare-for-all and proposed a major tax-credit for the middle class. AP Who could be running against Trump in 2020? Elizabeth Warren The Massachusetts Senator has formally launched her bid for president in 2020. A progressive Democrat, she is a major supporter of regulating Wall Street. AP Who could be running against Trump in 2020? Beto O’Rourke The former Texas congressman told Oprah Winfrey that he “has been thinking about running for presidency”, but stopped short of formally announcing his bid to run in 2020. AFP/Getty Who could be running against Trump in 2020? Wayne Messam Mayor of the city of Miramar in the Miami metropolitan area, Wayne Messam has announced his bid. He intends to run on a progressive platform against the "broken" federal government. He favours gun regulations and was a signatory to a letter from some 400 mayors condemning President Trump's withdrawal from the Paris Climate Accord. Vice News Who could be running against Trump in 2020? Kirsten Gillibrand The New York Senator formally announced her presidential bid in January, saying that “healthcare should be a right, not a privilege.” Getty Who could be running against Trump in 2020? Cory Booker The New Jersey Senator has announced that he will be running for the presidency in 2020. If he secures the nomination he said finding a female vice president would be a priority. Getty Who could be running against Trump in 2020? John Delaney The Maryland congressman was the first to launch his bid for presidency, making the announcement in 2017. AP Who could be running against Trump in 2020? Julian Castro The former San Antonio mayor announced his candidacy in January and said that his running has a “special meaning” for the Latino community in the US. Getty Who could be running against Trump in 2020? Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but is likely to face tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad. Getty Who could be running against Trump in 2020? Andrew Yang The entrepreneur has announced his presidential candidacy, and has pledged that he would introduce a universal basic income of $1,000 a month to every American over the age of 18. AFP/Getty Who could be running against Trump in 2020? Marianne Williamson The author and spiritual advisor has announced her intention to run for president. She had previously run for congress as an independent in 2014 but was unsuccessful. Getty Who could be running against Trump in 2020? John Kerry The former secretary of state has said he is still thinking about whether to run. Getty Who could be running against Trump in 2020? Michael Bloomberg The entrepreneur and former New York mayor– with a net worth of around $50bn – has said he will decide by the end of February whether to seek the presidency. AFP Who could be running against Trump in 2020? Howard Schultz Former Starbucks CEO Howard Schultz has not yet ruled out running for president in 2020, despite criticism that his bid could help re-elect Mr Trump by dividing the Democrat vote. AP Who could be running against Trump in 2020? Eric Holder The former attorney general has said he will decide in “the next month or so” whether to run as a 2020 presidential candidate. AP Who could be running against Trump in 2020? Eric Swalwell The California congressman said he is “ready to do this” and will decide before April whether to run. MSNBC Who could be running against Trump in 2020? Terry McAuliffe The former Virginia governor, who worked to elect Democratic governors during 2018 midterms, said there was a “50 per cent” chance he would run. AP Who could be running against Trump in 2020? Sherrod Brown The Ohio senator is still undecided about whether to run for president in 2020. Who could be running against Trump in 2020? Mitch Landrieu The former New Orleans mayor said he doesn’t think he will run for president, but “never say never”. AP Photo/Jacquelyn Martin

As Ms Warren has prepared for a presidential run, she has expanded the top ranks of her staff to include minorities in key positions. In the spring, she added Christopher Huntley, who is black, as her speechwriter. He previously worked for Representative Barbara Lee (D-Calif).

Over the summer, she hired Anne Morris Reid, a former Obama administration official who is black, as a senior adviser in her Senate office; Ms Reid was recently named chief of staff. LaToia Jones, a black Democratic strategist, has acted as a consultant for the past year.

Ms Warren, whose two Senate victories relied on help from minority voters, has in turn been loyal to her minority staff. Dan Rivera, mayor of Lawrence, Mass, helped her with Latino outreach. He won his race after she endorsed him over a sitting Democratic mayor.

Ms Warren also backed former campaign staffer (and her former law student) Michelle Wu in her successful bid to became Boston City Council's first Asian American member.

Ms Warren's efforts to demonstrate her affinity for black voters and their leaders have had mixed results.

A high point in their relationships came in the summer of 2015, when Ms Warren stood on a stage at a meeting of liberal activists in Phoenix and uttered the controversial words the party's then-presidential candidates, Mr Sanders and Ms Clinton, were struggling over: "Black Lives Matter".

She followed up in September 2015 with a speech on racism at Harvard University that was hailed as a "landmark" speech by the liberal magazine The Nation.

But some remaining awkwardness was on display earlier this month at the Capitol, when she and the Congressional Black Caucus chairman, Representative Cedric L Richmond (D-La), held a news conference about his plans to introduce a House version of Mr Warren's $500bn (£400bn) bill intended to vastly increase affordable housing.

Ms Warren focused on the camera angle, instructing Mr Richmond and Representative Gwen Moore (D-Wis), who is also black, to "come stand behind" her from the podium. Later, when Ms Moore's face was obscured by another speaker, Ms Warren extended her right hand and physically pulled the Wisconsin Democrat closer to her and into the spotlight.

The theatrics did not bother Mr Richmond. In a brief interview, he brushed aside the lasting impact of Ms Warren's DNA test. "In communities of colour, we look at your body of work," he said. "We don't look at one blip in time. Her body of work is a body of work that is very supportive of minority communities."

During the news conference, he labelled Ms Warren a "policy genius" and said later the two frequently text each other - evidence that some of Ms Warren's outreach has been fruitful.

"We just swap ideas often," Mr Richmond explained.

US Senator Elizabeth Warren tells Ben Carson he should be fired

Mr Richmond was her host last August at a town hall meeting at Dillard University in New Orleans, at which Ms Warren's off-the-cuff rhetoric about race turned into an issue for her November re-election campaign.

"Let's just start with the hard truth about our criminal justice system," Ms Warren said during the town hall. "It's racist. I mean, all the way. I mean, front to back."

Republican opposition researchers clipped those remarks into a short video, which became fodder for police unions in Massachusetts and for her Republican opponent, Geoff Diehl, who insisted she was "calling our law enforcement officers racist".

Even some of Ms Warren's black supporters in Massachusetts were taken aback.

"Some people were offended by it," said Suffolk County Sheriff Steve Tompkins, who worked on Ms Warren's 2012 Senate campaign before launching his own political career (with her endorsement). "I think folk of colour took it with a grain of salt. If you're black or Latino, it can be tough out there."

Ms Warren stuck closely to her prepared speech last week when she gave a commencement address at Morgan State University, a historically black university in Baltimore.

"We need to stop pretending that the same doors open for everyone. Because they don't," Ms Warren said, prompting applause.

"Rules matter, and our government - not just individuals within the government, but the government itself - has systematically discriminated against black people in this country."

She talked about predatory lending and discriminatory housing policies that have hurt black communities, and she earned rave reviews from African American attendees.

"She was right about how some people in Washington, DC, are treating us a little bit differently," said Arnold Nelson, 57, of New York. "She gets it. She understands us."

But there is a difference between appreciating the speech and being ready to back a presidential bid. One audience member said the flap over Ms Warren's DNA test should disqualify her from the presidential field.

"We need somebody squeaky clean to run in 2020 to ensure a victory over this anti-constitutionalist president," said Kevin Bailey, 63, who came to see his daughter graduate.

The DNA test hit him personally, he said.

"I did my DNA, and I'm 19 per cent English," said Ms Bailey. "But I can't claim I'm white."