Former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE's entry into the 2020 Democratic presidential race is increasing the pressure on Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.) to make inroads with black voters.

Sanders has been well aware of his need to attract support from African Americans, and he’s sought since entering the race to fix a problem that impaired him in 2016, when he ran a tougher than expected primary challenge against Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE.

Clinton was greatly helped in her victory by black votes. She won them by more than 70 percent over Sanders.

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The former secretary of State, New York senator and first lady was a proven commodity to black voters in 2016 who benefitted from the affinity many African Americans held toward her husband, former President Clinton.

Biden, who on Sunday appeared at a Baptist church in South Carolina, represents a similar threat to Sanders given the eight years he served as vice president to former President Obama — the nation’s first black president.

While Sanders is doing well in polls of white voters and progressives, the African American base of the party has not rallied to his campaign — at least not yet.

A Morning Consult poll released last week showed that 47 percent of black women said Biden was their top choice to be the Democratic nominee, while 18 percent said they preferred Sanders.

A poll from Quinnipiac University last week found Biden getting the support of 42 percent of nonwhite respondents. Sanders trailed Biden and Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.), getting just 7 percent support among nonwhites.

It’s possible those numbers to some extent reflect voters' familiarity with Biden, but they are worrisome nonetheless to the Vermont Independent’s allies.

“We have some work to do,” one Sanders ally acknowledged. “I don’t see a way for us to win the nomination without support from African Americans. If Biden picks up state after state in the South, it’ll make it really difficult for us.”

At multiple campaign events, Sanders has highlighted his push for economic equality as a way of reaching to African Americans, including his support for "Medicare for All," an increase in minimum wage and free college tuition.

Those policies could all narrow the racial wealth gap, though none of them are aimed specifically at black Americans.

On an issue that does affect black Americans specifically, Sanders shifted his position on reparations by saying he endorsed federal legislation to study the issue.

Just as notably, Sanders has sought to highlight his support for the civil rights movement.

His campaign schedule has also included stops in Selma, Ala., where he marked the 54th anniversary of “Bloody Sunday,” and in North Charleston, S.C., where he held a rally at a Baptist church. Sanders also was a featured guest at Rev. Al Sharpton’s National Action Network forum in New York.

One Sanders aide said the campaign is “focused on Bernie’s message of economic, social, racial and environmental justice” and pointed to outreach to community leaders, including faith-based leaders, racial justice activists, black colleges and universities, and business leaders.

“Bernie has a long track record of policy to address inequalities, and we plan to build on that with more proposals to further address issues facing the black community and going directly to communities impacted,” the aide said.

“We are taking no state, community, or constituency for granted as part of our effort to build a movement to transform politics in this country and create a government that works for everyone,” the aide added.

Sanders has stumbled as he has sought to appeal to black voters.

The most recent example came at the She The People forum in Houston late last month when he was asked about what he believed the federal government's role was in fighting the rise of white nationalism and white terrorism and how he planned to lead on the issue.

Some members of the audience booed after Sanders responded by saying that the nation needed to stand up against President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE's "demagoguery." After one of the moderators again asked the same question, Sanders began speaking about marching with Rev. Martin Luther King Jr., an answer that provoked more booing.

The woman who asked Sanders the question, Sayu Bhojwani, the president and founder of New American Leaders, told CNN she was unsatisfied.

"I didn't feel that we were being seen or heard," she said.

Basil Smikle, a Democratic strategist who served as the executive director for the New York State Democratic Party, said Sanders needs to better articulate policy areas that could help black communities.

“Sanders needs to depart from more egalitarian language and articulate a clear understanding of how public- and private-sector policies have hurt black Americans and how he intends to move the levers of government to solve them as president,” Smikle said.

“One would think he’d be adept at tailoring his populist message to embrace African American policy prescriptions, but he seems content to cede that ground to his opponents or is just unable to pivot towards race-specific policy,” Smikle added.

The Sanders ally maintained that Sanders learned his lesson from the 2016 race when it comes to black voters, pointing to comments Sharpton made about Sanders.

“I can say in the two years since, he has lived up to everything he has said to me and more. I want you to know he has done what he said,” Sharpton said last month.