That doesn’t mean the left didn’t contend with internal racism. In 1931, Communist Party member August Yokinen denied black members entrance to a dance. In what now sounds like a conservative caricature of progressives, the Party convened a trial in Harlem where Yokinen was charged with “white chauvinism.” Convicted and expelled from the Party, Yokinen was readmitted after six months of earnest work with the League for the Struggle for Negro Rights.

“The Left offered black writers the institutional support they could get nowhere else in white America,” Washington writes. “When mainstream literary publications completely ignored black culture and black life, the Marxist, leftist, and communist journals covered, theorized, and critiqued African American cultural production.” It bears constant repeating that Washington is not using “leftist” and “black” as mutually exclusive descriptors.

In the wake of the 1917 Russian revolution, the global left did not embrace any sort of “class over race” theory; the party line was much more sophisticated. In 1928, the Communist International, encouraged by black comrades, called not only for full racial equality, but “self-determination in the Black Belt” — freedom from America for a repressed nation of Southern blacks. It was an early endorsement of black power, and the Party backed it up with resources.

In her book “ The Other Blacklist ” (out in paperback later this year), Mary Helen Washington starts with a hole in American national memory: “Although the Left was by all accounts the most racially integrated movement of [the 1940s and ‘50s],” she writes, “the terms ‘U.S. radicalism,’ ‘left-wing,’ ‘Old Left,’ ‘New Left,’ and ‘communism’ came to signify white history and black absence.” Washington takes the reader back to a time when “the [Communist] Party was such an accepted organization that when a black family feared an eviction, it was not unusual for them to tell their children ‘find the Reds.’”

There’s a long history of pitting these two “poles” against each other, but it’s based on a few misconceptions. It’s true there’s a conflict; it’s just not between the left and blacks.

When Black Lives Matter protesters Patrisse Cullers and Tia Oso interrupted presidential candidate Bernie Sanders at the Netroots Nation gathering on July 18, the media had a frame ready: class against race, socialism against black power, all lives against black lives. At this site, Ned Resnikoff wrote , “two major poles of the modern progressive movement — the racial justice movement and the economic reform wing — crashed into each other.”

The Yokinen trial set up the Party as a credible anti-racist organization, and black interest increased rapidly. Later that year when nine black teenagers were accused of raping two white women on a train in Alabama, the Scottsboro Boys accepted help from the Party’s legal arm, turning down Clarence Darrow and the NAACP. Pictures of angry southerners waving “RACE MIXING IS COMMUNISM” protest signs look funny and incongruous now, but neither side was joking. After the Party mobilized to Birmingham, Alabama, for the Scottsboro case, a Klu Klux Klan flyer threatened “Negroes beware: do not attend communist meetings.” When Party organizers met anyway (900 blacks and 350 whites according to state records, flouting local segregation laws), they did so facing down the entire police department and three machine guns.

There are whispers of this past that haven’t disappeared: Take Fidel Castro celebrated in Harlem in 1960, the songs of Paul Robeson, the writing of W.E.B. DuBois, a Soviet anti-lynching poster, Derek Luke on The Americans. But the “two poles” story is the dominant history. It didn’t happen this way by accident. Mary Helen Washington unearths concerted efforts by the American government to sever the black-red connection by any means necessary.

On the cultural front, the Central Intelligence Agency funded anti-communist black and white organizations through the “Congress for Cultural Freedom (CCF).” White publications such as The Partisan Review and The Paris Review accepted money from the CCF and popularized a non-revolutionary moderate-left aesthetic. Meanwhile, law enforcement harassed and harangued Communists, especially black Communists, making it virtually impossible for them to continue any work in peace. As the Party was marginalized, black and white radicals developed new organizations.

Except as outsider bogeymen, American Communists have been more or less deleted from United States history. This redaction has erased a long tradition not just of left-black alliance, but black leftism itself. Today, we have democratic socialists such as Bernie Sanders who aspire to work within the American system, not overthrow it. Needless to say, revolution and black power are not on their agenda.

For its part, the American democratic socialist tradition — distinct from the Comintern line — always had its naive “two pole” elements. In 1903, socialist presidential candidate Eugene V. Debs wrote, “Let [blacks] settle the Negro question in their way, if they can. We have nothing to do with it, for that is their fight. We have simply to open the eyes of as many Negroes as we can and bring them into the Socialist movement.” As for black self-determination: “We have nothing special to offer the Negro, and we cannot make separate appeals to all the races.” This is “all lives matter” logic at its clearest, and it lacks the sophistication of the Black Belt thesis, in which black liberation as such is a vital part of a universal fight for justice.

None of this is to say the Party’s anti-racist functioning was perfect. There’s no doubt that later on, “white chauvinism” trials were used as cover by white Party members to jockey for power. But that doesn’t change the urgent need, as present now as it was in 1928, to put black power at the center of American leftist strategy.

"The Other Blacklist” poses a provocative question: Is America mentally equipped to recognize a black-led left? Is the “two poles” idea so embedded in our political imagination that we can’t recognize the universal call in “black lives matter”? I don’t imagine we’ll see a resurrected American Communist Party, but anyone who would call themselves a leftist is obligated to learn from its buried history.

The conflict between Sanders and Black Lives Matter — and the longer conflict between democratic socialism and black power — is thus not one between the left and black Americans. It’s between one theory of universal liberation and another, between a race-blind reformism and a shard from a shattered revolutionary tradition.

Here’s what I saw happen in the videos from Netroots Nation: Democratic presidential candidate Bernie Sanders was shouted down by the left.