(CNN) When Republican leaders shut down Elizabeth Warren's attempt to read Coretta Scott King's 1986 letter condemning Jeff Sessions on the Senate floor in February, they unknowingly opened a door for the Massachusetts senator to broaden her appeal as a leader in the Democratic resistance to President Donald Trump.

In the months since then, Warren has increasingly added a focus on racism and cultural issues to her signature economic populism over several major speeches -- while also developing new relationships with black leaders across the country.

Among them is Bernice King, the youngest daughter of Martin Luther King Jr. and Coretta Scott King. The two spoke by phone, exchanged numbers and then met privately in Atlanta when Warren was in town for a progressive gathering.

"In order for us to make effective change, leaders have to be courageous. They have to be willing to take a stance ... willing to lose some things," King said in an interview. "And she was willing to risk some things in this process, being silenced on the floor."

On Monday, Warren will meet King for a second time this month in Atlanta, where she'll participate in The King Center's "Beloved Community Talks" event, set for 6 p.m. ET at Ebenezer Baptist Church.

The speeches have stoked speculation that Warren is angling to run for president in 2020. And while the Massachusetts senator is careful not to even hint at a run herself, she paused only briefly and smiled as chants of "Warren 2020" rose up during her speech at Netroots Nation.

"People talk about her in presidential terms often when I travel the country, and I think in the African-American community, it's because they appreciated that she, in a very full-throated way, will speak to the issue of racism," said Michael Curry, who chairs the national NAACP's advocacy and policy committee and was until recently the NAACP Boston chapter president.

The Bernie Sanders problem

As Democrats search for new leaders in the Trump era, Warren's long-held hero status among progressives and economic populists would give her a foothold should she seek the party's presidential nomination.

But Vermont Sen. Bernie Sanders appeals to a similar group of voters. And his 2016 campaign against Hillary Clinton was doomed in part by his inability to win older black voters in the South.

His failings have left Democratic operatives gaming out the 2020 race with a basic question about Warren: How is a white Harvard law professor who grew up in Oklahoma going to do what Sanders couldn't?

Some black leaders say they see major differences in Sanders' early 2016 candidacy and Warren today.

"When Sanders ran, he was very distant and had to learn how to relate to blacks," said Rev. Jesse Jackson.

Warren represents a more diverse state, and "she does not talk with a strain; she talks with a comfort level and familiarity" in speaking with black leaders, he added.

Jackson said he and Warren speak "semi-regularly" and that the two have "open access to each other." In July, he hosted Warren in Chicago for a speech to the Rainbow PUSH Coalition, a civil rights and political activist group he founded, where Warren hammered a legal system that fails to deliver justice when "black men and women die at the hands of those sworn to protect them" and warned of GOP efforts to restrict voting access.

In Warren, Jackson said he sees an economic message -- and a delivery -- that carries few cultural limitations. "The best news is that these issues affect whites in Appalachia and blacks in the Delta," he said.

Still, Warren has made few trips South, to states like South Carolina, which votes third in the Democratic presidential nominating contest and is the first real gauge of candidates' support among black voters.

"These communities don't forget who their friends were," said Jaime Harrison, the former chairman of the South Carolina Democratic Party. "They don't suffer fools -- they have a test when they know that people are just coming in and they haven't spent the time to build the network and the connections,"

"Harping on anti-trust and Wall Street is not going to cut it," Harrison said. "In some communities, the economic anxiety is not talking about how much money people are making on Wall Street. Economic anxiety is, no infrastructure, therefore no jobs, and the schools are crap. Therefore their kids, if they get any education, they leave the town and then the state and they never come back."

Attacking Trump in Detroit

Warren's increasing focus on racial and cultural issues began to emerge in April, when she spoke at a major dinner hosted by the NAACP's Detroit branch.

There, Warren said Trump has "stirred up some deep ugliness in the United States," and she accused Attorney General Jeff Sessions -- the subject of the Coretta Scott King letter -- of being on "a mission to turn the clock back 157 years."

"The fight against racism and inequality and ugliness in all its forms is a righteous fight," Warren said. "I came to Detroit to say I will be part of that fight."

The remarks struck Warren's allies, who saw her aggressively confronting issues of race in front of an audience of thousands of black leaders from across the country.

"I saw in her speech an intentionality to speak to our communities -- to say, 'I'm here for you, and I plan to be a champion on the issues you care about,'" said Curry, the NAACP board member from Boston.

"I think being on that particular stage gave her an opportunity to deliver that message to a larger group of African-Americans," Curry said.

Steering the Democratic Party

Warren moved her cultural messaging beyond a defensive, anti-Trump posture and toward guiding the Democratic Party forward during a closely watched speech at Netroots Nation, the progressive gathering in Atlanta in early August.

Since the 2016 election, an emerging divide within the Democratic Party is between those on the left who prefer the message of all economic populism, all the time, and liberals who see issues of race, gender, sexual orientation, religion and other identity issues as central.

"In the wake of the last election, I've heard people say we need to decide whether we're the party of the white working class or the party of Black Lives Matter," Warren said.

"I say we can care about a dad who's worried that his kid will have to move away from their factory town to find good work -- and we can care about a mom who's worried that her kid will get shot during a traffic stop," she said. "The way I see it, those two parents have something deep down in common: The system is rigged against both of them -- and against their kids."

Warren also took a dig at Bill Clinton-era policies that are largely seen as corrosive among black voters, declaring that "the Democratic Party isn't going back to the days of welfare reform and the crime bill."

In every speech, Warren doesn't mention Trump's nickname for her, "Pocahontas" -- a jab at her Native American heritage. But she harkens back to the moment on the Senate floor, when Majority Leader Mitch McConnell, R-Kentucky, said that Warren had been warned against reading the Coretta Scott King letter, but "nevertheless, she persisted."

Warren, who is up for reelection in Massachusetts in 2018 and has been careful not to feed into 2020 speculation, declined to be interviewed for this story, emailing a statement instead.

"Divide and conquer is an old story in America -- the idea that whatever worries you, the answer is to blame others who don't look or talk or worship like you do," Warren said in the statement.

"But when we turn on each other, we can't unite to fight back against a rigged system," she said. "President Trump's divisive actions don't reflect our values. We need to say so -- and we need to keep fighting every single day to help build opportunity for every single American."

The view from Massachusetts

In Boston, black leaders credit Warren with accessibility and say she is eager to dive into the details of issues with a disproportionate impact on minorities.

"There is almost no issue that impacts communities of color that many of us have not had a conversation directly with her," said Curry. "She is abnormally accessible to stop on the street or to catch her in DC and have really detailed conversations around issues that African-Americans care about."

"What you're seeing on the national stage is what I've seen many times in intimate rooms and spaces with Sen. Warren," said Ayanna Pressley, a Boston city councilwoman.

Pressley said she has worked closely with Warren to combat "predatory business practices" at for-profit colleges. She also spoke with Warren recently about the stigma about the cannabis industry that prevents banks from lending to minority small-business owners in the space.

"She does not marginalize the community," Pressley said. "She sees an African-American in their totality, and I appreciate that. She is inclusive. So I don't only get a call to come sit at a table about an issue that is disproportionately impacting communities of color. I'm invited into any room where she believes that my office ... or my lens could add value."

Warren, a former Sunday school teacher, also makes regular, unpublicized church visits.

"It wouldn't surprise me if she was in churches and worshiping and people didn't know she was there. She is just that consistent about her presence in these spaces," Pressley said.

At the African Methodist Episcopal Zion Church in Roxbury in February, Warren discussed the Senate's admonition over reading the Coretta Scott King letter criticizing Sessions.

"No one got up to defend his record and what he has done in the years since," Warren said about what transpired in the chamber, according to a Boston Globe account of the visit. "All they said was, 'Be silent, be silent, be silent,'"

'You have to show me'

In an interview ahead of Warren's visit, King said Warren's reading of her mother's letter about Sessions left her "filled with joy."

"I said, you know, 'Wow -- my mother's voice is coming forth, and she's been gone for 11 years now.' I'm always worried, are people going to remember her and her contributions?" King said.

King recalled that when her father was assassinated in 1968, he was planning a "Poor People's Campaign" for economic justice that was aimed at alleviating poverty across racial barriers. She said the fights that progressives take on today for an increased minimum wage, college affordability and mass incarceration are all issues that connect to a broader battle against economic injustice in which she sees Warren as a leader.

"Her having a strong economic message, combined with some of the cultural language and sensitivity to how these things play out in the African-American (community), is certainly critical," King said.

But, King added: "You also have to show me, as well."