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Bernie Sanders reached the pinnacle of his campaign inside Cowboys Dancehall in San Antonio on Feb. 22. He pumped his fist to punctuate a triumphant speech. He’d just won the Nevada caucuses and was sitting on top of the Democratic presidential race.

But 1,200 miles away in South Carolina, some aides and allies felt dread that trouble was lurking just around the corner. “I knew that our campaign had not done the work it needed to do,” Donald Gilliard recalls thinking. He felt the campaign’s strategy was “geared toward white progressives,” leaving black voters behind.

Gilliard, the deputy state political director, wasn’t alone. Mal Hyman, a former congressional candidate and a Sanders surrogate in South Carolina, had a similar sense of anxiety. “We knew we were vulnerable,” he lamented.

A week later, their worst fears came true. A resurgent Joe Biden thumped Sanders by 28 points in the South Carolina primary, sending the Vermont senator into a free fall from which he has not recovered.

The loss underlined one of the fundamental failings of the Sanders campaign: He was unable to win the trust of African American voters. As the 78-year-old democratic socialist considers how long to continue his historic campaign, his disconnect from black voters threatens to sharply limit his influence in a party that is soon expected to belong to Biden.

Now some who worked on the front lines of his campaign, including black staffers and surrogates, are speaking out about what they believe was a negligent strategy that underestimated the significance of the first primary with a majority-black electorate — a blueprint they said they tried and failed to redirect, and one that ultimately put the campaign on a devastating trajectory.

Sanders sees the United States through the prism of class, but the 2020 primary has in some ways reaffirmed that for many Americans, the racial divide is more urgent. The senator built a coalition of millennials, working-class whites and Latinos, wagering that a strong showing in the first three states — none of which has many black voters — would power him through South Carolina and beyond.

As a result, many African Americans felt disconnected from him. “I think the distinguishing attitude for Sanders, that you didn’t see associated with Biden, was an angry white man,” said Ivory Thigpen, a state representative who served as co-chair for Sanders in South Carolina and believes strongly in his message. “In the African American culture,” he said, “nonverbal communication and body language is huge.”

Conveying a personal touch was never Sanders’s strength, Thigpen added. But he added, “I think being accessible would have made up for it.”

Sanders campaign officials defend their efforts, saying the complaints of their South Carolina operatives do not reflect the tough choices the campaign faced nationally or the challenge of dislodging black voters’ long-standing loyalty to Biden — which was only strengthened by a last-minute endorsement from influential Rep. James E. Clyburn (D-S.C.).

“This campaign nurtured and put African Americans in the pipeline of a presidential campaign,” said Nina Turner, a national co-chair of the Sanders campaign. Turner, who is black, attributed the complaints to state officials who had “the luxury to only be singularly focused,” while she, Sanders and other top campaign officials “had to focus on the nation.”

The campaign had other big problems, according to current and former officials and allies. The team was caught flat-footed by how quickly the Democratic Party establishment united behind Biden, after the campaign executed a plan that rested heavily on a divided opposition. Sanders has a tendency to micromanage, some said, slowing big decisions. And aides’ efforts to get him to criticize Biden more directly fell short.

But the moment that many keep replaying in their minds is the painful defeat in the Palmetto State. It came just a week after Sanders had become the undisputed primary leader with his decisive win Nevada, following strong showings in Iowa and New Hampshire.

“If we’d been a little bit closer in South Carolina, we would have the momentum instead of Biden going into Super Tuesday,” said Raymond Corley, who served as political director for the Sanders campaign in South Carolina. Black voters in the state backed Biden over Sanders by a margin of 61 percent to 17 percent, according to network exit polls — a yawning gap that was largely repeated in other primaries.

Sanders, an irascible Northeastern liberal, was never a natural fit with many black voters, particularly older ones in Southern states with more-conservative leanings. But several staffers said the disconnection did not have to be this bad.

Turner, a former Ohio state legislator and Sanders’s most visible African American ally, traveled with Sanders, introduced him at rallies and helped shape the campaign’s outreach to black voters — including keeping an eye on South Carolina.

Some staffers felt she was wrong for that role. “She didn't know the state,” said Gilliard, who said he is fond of Sanders but parted ways with the campaign after the Feb. 29 primary.

Turner said the campaign relied heavily on local talent, including Gilliard. “I have a keen understanding of the black community,” she said. “The overwhelming majority of [South Carolina staffers], including him, understood the state. And he was hired to do a job.”

But the chain of command was murky, according to some staffers and surrogates. Thigpen recalled telling Turner privately that campaign officials discussed things that didn’t end up happening, and he often felt like he was “going to customer service and saying, ‘Hey, I want this done.’ ”

Others who worked in the state said some of the campaign’s decisions amounted to political malpractice. They faulted national campaign officials for deploying what they viewed as unseasoned strategists; not advertising more aggressively on television and black radio; and missing opportunities to bring Sanders in for face time with black leaders and voters.

Even more basic needs such as yard signs became a source of angst, they said, citing a stark shortage in a state where visibility is a big part of the political culture.

“Inexperienced state leadership,” said Hyman, who gave speeches for Sanders, “was very slow to respond and to take any risk or broaden our base or to push for some of the what we thought were common-sense suggestions.”

One idea, for example, was for Sanders to visit with a convention of Baptist ministers, according to Gilliard and Thigpen, who said that plan was rejected by higher-ups. Jessica Bright, who served as state director, said the decision was “more of a scheduling conflict. It wasn’t anything outside that realm.”

But for people in South Carolina, Sanders’s priorities clearly appeared to be elsewhere. The campaign didn’t start advertising heavily on radio in the state until late January and on television in mid-February, according to data from Advertising Analytics, even though the primary was Feb. 29.

It was no secret inside the campaign that the South Carolina operation was troubled.

Turner and another senior adviser, Chuck Rocha, traveled to the state to address personnel turmoil last summer, according to people with knowledge of the situation. In November, the campaign parted ways with then-state director Kwadjo Campbell, replacing him with Bright, who had been his deputy. Marvin Hayes, an operative from Ohio, was brought in as a senior adviser the previous month.

Just before he departed, Campbell sent an explosive memo to Sanders, Turner, campaign manager Faiz Shakir and other top officials excoriating their decisions, according to people with knowledge of the communication.

“I have not been able to do my job of building a base in the African-American community because of interference from National on a number of critical strategic decisions that have impeded our ability to gain traction among this key demographic needed for victory,” Campbell wrote.

He accused the campaign brass of preventing him from partnering with local African American candidates and of interfering with personnel moves.

Turner said that some of what Campbell suggested wasn’t even legal. “Some of the partnerships that he proposed did not comport with campaign finance laws,” she said, adding that many of his other ideas were “carried forward.” Campbell initially declined to comment. After publication of this story, he said it was “not illegal to have our volunteers team up” with volunteers from local campaigns.

In a joint telephone interview, Bright, Hayes and Michael Wukela, who was communications director in South Carolina, strongly disputed the notion that the campaign had not vigorously contested the state. Arguing that they had a more intense operation than Biden, they said that Sanders attended more than 70 events there, hired a field staff that was mostly people of color, and that the campaign knocked on the equivalent of a door a minute.

“I would say, without fear of contradiction, we had the best campaign operation and field operation in the state of South Carolina,” Hayes said. He suggested that Sanders’s poor performance was due to voters’ belief that Biden was more electable against President Trump.

“There was a lot of energy and attention being paid to the defeat of Donald Trump,” Hayes said, while “the important part of Senator Sanders’s message was about what is affecting people’s lives on a day-to-day basis.” On one visit to Denmark, S.C., for example, Sanders held small events on the subject of water contamination.

Few dispute that the South Carolina primary was the turning point in the primary campaign. In the following 72 hours, two of Biden’s rivals endorsed him, and a raft of Democratic officials jumped on board. Three days later, Biden swept most of the Super Tuesday races, including other Southern states with large black populations.

It was only after those humbling defeats that the campaign finally appeared to rethink its approach to black voters. Phillip Agnew, a well-known African American activist and campaign surrogate, was named a senior adviser. Turner and another official worked the phones for hours to secure an endorsement from civil rights icon Jesse Jackson.

But by that point, Sanders had little room to maneuver. He canceled a planned visit to a civil rights museum in Mississippi to campaign in Michigan, and then scrapped plans for a speech on racial justice. When a reporter questioned Sanders on his decision to skip a commemoration of “Bloody Sunday” in Alabama, he was curt, snapping that he was in California drawing a big crowd.

Sanders also paid a price for his reluctance to speak publicly about his role in the civil rights movement, some allies felt, despite having an impressive story to tell about impassioned activism that included an arrest at a 1963 protest.

In the eyes of some Sanders aides, there was little he could have done to reverse the loyalty that Biden spent decades building among black voters. Others felt that the campaign misjudged how impactful Biden’s institutional support would be. At the same time, a wipeout of nearly 30 points was hardly inevitable, some said.

“It kind of seems like an underestimation,” Thigpen said. “Not only of how important the African American vote was, but how much it was going to be a bellwether and an indicator to other African American populations in other states.”