While discussing his own racial “blind spots” during Sunday night’s Democratic presidential debate in Flint, Michigan, Sen. Bernie Sanders offered that white people “don’t know what it’s like to be living in a ghetto. You don’t know what it’s like to be poor.” His comment drew swift condemnation on social media, since it appeared that the Vermont lawmaker was implying that only black people live in impoverished communities, reinforcing inaccurate and painful stereotypes that have dogged African-Americans for years.

view photo essay The presidential campaign: Bernie Sanders The self-described democratic socialist is known for pushing change on income inequality, college affordability and criminal justice reform.

Sanders’ “ghetto” gaffe underlined a persistent problem that may have crippled his bid for the 2016 nomination. He has struggled to connect with black voters, and his choice of words has often undercut a populist economic message that might have resonated with people of color.

Even if Sanders had the best of intentions, it was not his best moment, as evidenced by one of his most prominent African-American surrogates — former NAACP chairman Ben Jealous — who told NBC News: “Sen. Sanders is from Burlington, he grew up in old Brooklyn, he knows white folks live in ghettos.”

On Monday, Sanders attempted to clarify his debate statement, telling a gaggle of reporters in Detroit: “What I meant to say, is when you talk about ghettos, traditionally what you’re talking about is African-American communities.”

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Sanders, who has been shellacked repeatedly by former Secretary of State Hillary Clinton among black voters in every 2016 contest to date, has aggressively tried to court African-Americans. He has worked references to criminal justice reform and voting rights into his stump speeches and debate talking points. He has boasted endorsements from black icons like Dr. Cornel West, Danny Glover and Harry Belafonte. He has even tried to soften his past positions on gun control, in a direct nod to concerns in communities of color about the shootings of unarmed black men. Of course, many white Americans know exactly what it’s like to “live in the ghetto.” Many, including immigrants have, do and did. — Joy Reid (@JoyAnnReid) March 7, 2016

But he appears to have hit a wall with black voters, and the resistance began early in his campaign.

It’s not lost on many African-Americans that Sanders hails from one of the most historically white states in the country. His base of support has been overwhelmingly white from the beginning, and when he was initially confronted by African-American activists, he fumbled badly. Last July, he got testy and exasperated when Black Lives Matter protesters disrupted his appearance at the progressive Netroots Nation conference in Phoenix.

“Black lives, of course, matter,” he said from the stage. “But I’ve spent 50 years of my life fighting for civil rights. If you don’t want me to be here, that’s okay.”

“I don’t want to out-scream you,” he added.

Sanders’ performance provoked a backlash. “What Bernie did is he treated them as hecklers instead of a movement,” Charles Chamberlain, the executive director of Democracy for America, told TIME afterwards.

Protesters proceeded to demand that Sanders mention the late Sandra Bland, who died in police custody under controversial circumstances in Texas, by name. He failed to do so, although he tweeted a reference to her the following day and later mentioned her in a debate as an homage to her family. But for many black voters, it might have been too little, too late. Bland’s mother wound up choosing to campaign for Clinton.

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Bland’s death was fresh on the minds of many African-Americans at the time. Dash cam video of her arrest had just been released, calling into question authorities’ narrative (they claimed she committed suicide in her jail cell) yet again. Sanders had actually been the first candidate to speak out on Bland’s arrest, calling the conduct of the officer who stopped her “police abuse,” but he still drew criticism for tending to pivot towards his comfort zone of economic inequality, rather than delve deeply into the issue of race.

“No one is arguing that Sanders literally doesn’t see race — they’re saying that Sanders sees racial inequality as less important than economic inequality and shouldn’t,” wrote Dara Lind for Vox at the time.

And most African-Americans are not poor. The AA poverty rate is too high, of course, at about 28%, but that’s not most or all. — Joy Reid (@JoyAnnReid) March 7, 2016 considerable debate, but few would dispute their adeptness at associating themselves with black causes and concerns.

Sanders has responded by tirelessly tying himself to the civil rights movement of the 1960s, a strategy which also may have backfired. He was undoubtedly active in campus protests on behalf of racial equality during the heyday of the civil rights movement, but simply having participated in the March on Washington doesn’t establish a relationship with modern black voters overnight.

And when civil rights icon Rep. John Lewis claimed he “never saw” Sanders at marches or when a widely circulated photo of what was thought to be the Vermont senator leading a sit-in protest has been disputed, it muddied his message at a time when voters of color were just starting to get to know him.

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One of Clinton’s attack lines on Sanders that has stung — that she is not a one-issue candidate — has also appeared to resonate with black voters. Even black voters on the far left were apoplectic that Sanders’ ambitious economic proposals stopped short when it came to reparations for slavery. And many black voters, who are hyper-sensitive to the degree of opposition President Obama has faced from conservatives, take issue with the notion that Sanders would somehow be more persuasive.

It didn’t help that some of Sanders’ most ardent white supporters are often guilty of “Bernie-splaining” to black voters about why they should be backing their candidate. “If only black people knew more, understood better, where the candidates stood — now and over their lifetimes — they would make a better choice, the right choice. The level of condescension in these comments is staggering,” wrote Charles Blow in a column for The New York Times in February. Blow went on to argue that black resistance to Sanders was not steeped in ignorance but pragmatism.

“Black folks don’t want to be ‘betrayed by too much hoping,’ and Sanders’s proposals, as good as they sound, can also sound too good to be true. There is a whiff of fancifulness,” he wrote.

As the Democratic 2016 primary campaign has chugged along, Sanders has not only learned to embrace Black Lives Matter, but he’s being forced to confront the reality that black votes matter, too. In order to win the Democratic nomination he cannot simply dominate with white voters. The problem is that he may have already lost black voters a long time ago.

Editor’s note: This piece has been updated with new comments from Sen. Sanders on Monday.