(CNN) A big story of the Democratic primaries is the rise of the so-called pragmatic black voters who revived former Vice President Joe Biden's flagging presidential campaign.

But there's a flip side to this story that no one is paying attention to:

What happened to all those radical black voters who should be rallying to Sen. Bernie Sanders' side?

Not many seem to know it, but there is a long and vibrant tradition of socialism and radical political leadership in the black community. Many of black America's most beloved and respected leaders were socialists.

The Rev. Martin Luther King Jr. was a socialist , according to many historians. W.E.B. DuBois was a socialist , and so were civil rights leaders A. Philip Randolph and Bayard Rustin . The most prominent black philosopher today, Cornel West, is a socialist and Sanders' supporter. Hip-hop artists, such as rapper "Killer Mike" and Chuck D of Public Enemy, are also big Sanders supporters.

There is arguably no group in America that should be more suspicious of unfettered capitalism than blacks. Slavery, for example, was driven as much by greed as racism. And blacks lost half of their wealth due to the 2008 economic collapse.

"You can't have capitalism without racism," Malcolm X once said.

So as he seeks to blunt Biden's momentum in Tuesday's primaries, why hasn't Sanders been able to tap more into this black radical tradition? And why don't more people know about it?

When every cool black leader seemed to be a socialist

African Americans used to hear socialist jargon all the time.

But "people aren't used to hearing it anymore," says Solomon Russell, a spokesman for a national group called the Black Socialists in America , when asked why Sanders' emphasis on class and race hasn't drawn more black support.

"If you go back to what was being talked about in the black power movement and the civil rights movement in the '60s, it's not dissimilar at all to what was being said."

Among black people, socialism was once fashionable.

Stokely Carmichael, the civil rights activist who coined the term "black power," changed his name to Kwame Ture in honor of two African socialists leaders.

The Black Panther Party, seen here marchng in 1968, was shaped by Marxism and was dubbed 'socialist to the core.'

The founders of the Black Panther Party -- best remembered for their berets, leather jackets and guns -- were inspired by socialism and Marxism as much as they were by the right to carry weapons.

It was not uncommon to hear black leaders talk about "working class solidarity," the "oppressed masses" and "revolution."

"Every major progressive social movement in this country has had a lot of socialists in it," the historian Michael Kazin recently said in a New Yorker interview.

Even the Communist Party, vilified by many Americans, was viewed with sympathy in parts of the black community.

During the Jim Crow era, blacks such as Richard Wright, acclaimed author of "Native Son," joined the Communist Party in part because it had a reputation for speaking up for racial justice when America's two major political parties were largely silent.

It was the American Communist Party, for example, that helped lead the defense of the Scottsboro Boys, a group of nine young black men who were falsely accused in 1931 of rape by two white women and all but one were sentenced to death by all-white jurors.

How Sanders defines his socialism

"Socialism isn't a dirty word to African Americans," says Jerald Podair, an author and history professor at Lawrence University in Wisconsin. "I'm not saying that all African Americans are socialists, but ... they're not going to have this 'I smell something bad' reaction to the word."

Democratic presidential candidate Sen. Bernie Sanders speaks to voters as philosopher and social activist Cornel West listens during a campaign rally in Iowa.

A recent poll backs Podair up. Almost two thirds — 65 percent — of African Americans have positive impressions of the term socialism, compared to 35 percent of whites, according to the Pew Research Center.

Socialism is, however, still a misunderstood word. That may be part of Sanders' challenge.

Sanders calls himself a "democratic socialist." In a speech last year , he defined what it means to him. Just as the Bill of Rights guarantees people political rights, every person should have basic economic rights: quality health care, a good education, a good job with a living wage and a clean environment, he said.

Democratic Socialists point to examples such as Canada's national health care system, France's nationwide childcare program and the wide-ranging welfare state in Sweden as models of democratic socialism.

"We must recognize that in the 21st century, in the wealthiest country in the history of the world, economic rights are human rights," Sanders said at the time. "That is what I mean by democratic socialism."

Sanders and Dr. Martin Luther King Jr.

Sanders has tried to blend calls for both economic and racial justice.

His campaign website is filled with calls to treat "structural racism" and eliminate mass incarceration. He's talked about being arrested for resisting segregation, and he invoked King in one of his most recent speeches when he said:

"When Trump attacks socialism, I am reminded of what Dr. Martin Luther King, Jr. said: 'This country has socialism for the rich, rugged individualism for the poor.' ''

Sanders' invocation of King is a shrewd move. There is arguably no more revered leader in the black community.

Yet many still do not know King is widely considered a Democratic Socialist. Given the political realities of his time, King could not have publicly admitted that he was a Democratic Socialist. His enemies frequently called him a communist and the FBI targeted King with harassment and a lengthy smear campaign.

The Rev. Martin Luther King Jr., spoke with admiration about Democratic Socialism and is widely considered a socialist by historians.

But King often talked like a socialist. In a speech he gave one year before he died, King said the civil rights movement must address "restructuring the whole of American society," and ask questions "about a broader distribution of wealth."

"You see, my friends, when you deal with this, you begin to ask the question, 'Who owns the oil?' You begin to ask the question, 'Who owns the iron ore?' You begin to ask the question, 'Why is that people have to pay water bills in a world that is two-thirds water?' ''

When King traveled to Norway in 1964 to receive his Nobel Peace Prize, he talked with open admiration about the economic systems in that country and in neighboring Sweden.

King was even drawn to socialism as a young man.

In a letter to his then-future wife, Coretta Scott, a 20-something King wrote:

"I imagine you already know that I am much more socialistic in my economic theory than capitalistic. And yet I am not so opposed to capitalism that I have failed to see its relative merits... So today capitalism has outlived its usefulness. It has brought about a system that takes necessities from the masses to give luxuries to the classes."

King's last project is one of the best examples of his socialist beliefs. His "Poor People's Campaign" proclaimed goals that are now associated with Democratic Socialism: a guaranteed national income, universal health care and a federal jobs program.

"Had he lived, at some point King would have said, 'I am an African American socialist,' " says Podair, the historian.

So what happened to the radical black tradition?

Why don't more people today hear about this radical tradition in the black community? It's been obscured by a constant focus on "pragmatic" black voters in the Democratic primaries.

Black Lives Matter co-founder Patrisse Cullors speaks at a Bernie Sanders 2020 presidential campaign rally in Los Angeles earlier this year.

Russell, the spokesman for the Black Socialists in America, cites another reason: The grim historical lessons many blacks draw from any attempts at radical political change.

Many of the black community's most radical leaders were either assassinated or their organizations destroyed by the FBI's counter-intelligence program , he says. The rise of conservativism in the years following the civil rights movement also cooled the revolutionary fervor in the black community, he says.

"The arresting and jailing and murder of black organizers and leaders was seen as a lesson not to go that path again," Russell says.

History makes another lesson clear for many black voters: Lasting radical change often comes disguised in a series of smaller steps, another historian says.

"Even when slavery was abolished, it was incremental -- it began with the Emancipation Proclamation, and led up to the 13th Amendment," says Ravi Perry, chair of the political science department at Howard University in Washington. "Same thing with civil rights. We didn't just have one huge sweeping bill that changed everything. First we focused on public transportation, then voting rights, then fair housing. There were incremental steps."

Radicalism doesn't mean much if you lose

Black voters flocking to Biden also realize something else, Perry says:

"You can't do anything until you win first. Many who did not vote in 2016 or stayed home or voted for (Green Party nominee) Jill Stein, I think many of them learned their lessons."

Sanders must address these challenges if he is going to fare better with black voters in Michigan, Mississippi and the four other states holding primaries or caucuses Tuesday.

One way to describe the roadblock he faces in the black community is to recount an anecdote from the life of Carmichael, the civil rights activist who despised capitalism.

Carmichael was so committed to radical change that he'd answer each phone call with the same greeting: "Ready for the revolution." He was literally still talking about revolution on his death bed, at 57 from prostate cancer.

Sanders' weakness with African American voters does not mean the black community isn't ready for a revolution in the Trump era. But blacks' collective attitude in 2020 may best be described as this:

First, we need someone to beat Trump. Then we'll talk about the revolution.