ASSOCIATED PRESS/Ross D. Franklin The last time Sen. Bernie Sanders (I-Vt.) spoke at Netroots Nation — in Phoenix, Arizona, in July 2015 — he was interrupted by a Black Lives Matter protest.

PHILADELPHIA ― Nina Turner, a former Ohio state senator and top surrogate for Vermont Sen. Bernie Sanders’ 2020 presidential campaign, stood before a crowd protesting the impending closure of a hospital in the center of Philadelphia. “I stand here in solidarity with you this afternoon on behalf of Senator Bernie Sanders ― a champion for the people,” Turner told the crowd of over 800 hospital workers and their allies at a rally outside Hahnemann University Hospital, which serves a low-income population. Those assembled, many of whom held signs calling for “Medicare for All,” let out a roar the second they heard Sanders’ name, chanting “Ber-nie, Ber-nie, Ber-nie.” It was a perfect encapsulation of the grassroots campaign Sanders wants to run, and the enthusiasm he hopes to elicit from it.

But a lot of his staff are here and @ninaturner is the headliner. It fits with the movement/activism-driven focus of his campaign. Her speech doubles as a campaign speech. pic.twitter.com/SQVsoYkMZo — Daniel Marans (@danielmarans) July 11, 2019

But the warm reception obscured a tense reality beneath Turner’s visit. She was there in Sanders’ stead. Sanders was neither at the protest, nor will he be attending a presidential candidate forum on Saturday at Netroots Nation, the country’s largest gathering of progressive activists, which is taking place a block away from the hospital where Turner spoke. Someone involved in organizing the forum told HuffPost that Sanders was reconsidering attending as late as Wednesday night, a claim that the Sanders campaign flatly denied. Of course, Sanders is not the only major presidential candidate skipping the liberal confab. The lineup for the conference’s presidential candidate forum is due to feature only Sens. Elizabeth Warren (D-Mass.) and Kirsten Gillibrand (D-N.Y.), former Housing and Urban Development Secretary Julián Castro, and Washington Gov. Jay Inslee (D). But Sanders’ absence was noteworthy both because of his ordinarily deep ties to the progressive activist community, and his troubled history at Netroots. In July 2015, shortly after he launched his first presidential run, Sanders was interrupted by Black Lives Matter protesters during his speech at Netroots in Phoenix, Arizona. They chanted “black lives matter” and “say her name,” a reference to Sandra Bland, a black woman who had recently committed suicide in police custody. Sanders responded, “Of course black lives matter.” But he was obviously irritated and, after citing his work in the civil rights movement, insisted on continuing his speech. For his critics, the moment came to exemplify the difficulty he had reaching black Democratic voters and incorporating racial justice issues into his message of economic inequality. Sanders has since worked to build closer relationships with African American leaders; made the unique challenges of racial injustice a more prominent theme in his new stump speech; and hired a diverse circle of senior staff. But his troubled relationship with some of the leading figures associated with Netroots continues. In particular, he has elicited bitter criticism from Markos Moulitsas, founder of the progressive news site Daily Kos, which is a major sponsor of the conference. “The problem with Bernie Sanders is that he has the exact same message he had four years ago,” Moulitsas said on NBC’s “Meet the Press” at the end of June.

ASSOCIATED PRESS/Charles Krupa Sen. Elizabeth Warren (D-Mass.), whom some progressive activists see as a more capable spokesperson than Sanders on racial justice, is due to speak at Netroots Nation on Saturday.

Sanders’ campaign told HuffPost that he is not attending Netroots due to conflicts in his campaign schedule and noted that many Sanders campaign staffers and surrogates are attending. (Indeed, the senator spoke Thursday at a presidential town hall held by the League of United Latin American Citizens in Milwaukee, Wisconsin.) A spokesperson for Netroots told The Daily Beast, however, that Sanders had considered attending but his campaign raised concerns about Moulitsas’ potential bias as a candidate forum moderator. Reached for comment on Friday, the Sanders campaign denied that the decision not to attend was the result of anything other than scheduling conflicts. It also said that its discussion with Netroots about the presidential candidate forum was not focused on Moulitsas, so much as it was a standard effort to discuss the panel’s themes. “We have a long and positive relationship with ... the whole Netroots team,” said Sanders campaign spokeswoman Sarah Ford. “Although Bernie’s schedule precludes his ability to attend, we wish the organizers and attendees a successful weekend and thank them for all their work to support progressive issues and activists across the country.” HuffPost obtained an email that Sanders’ campaign chief of staff Ari Rabin-Havt sent Netroots communications director Mary Rickles on Monday that appears to confirm the campaign’s version of events. “We wish we could make it, and we tried, but we couldn’t make the schedule work,” Rabin-Havt wrote. “Hope to do it next year, and let us know if we can ever be helpful.” In an interview with HuffPost on Thursday, Moulitsas repeatedly attacked Sanders and claimed the Vermont senator was divisive. At the same time, Moulitsas claimed he would have moderated the presidential candidate forum impartially. Moulitsas said that former Vice President Joe Biden — another no-show — would have had little to gain from attending the conference, since he is unlikely to win people over. Not so for Sanders, he argued. “He’s actually losing ground to Warren by any objective measure,” said Moulitsas, who has spoken very positively about Warren and Sen. Kamala Harris (D-Calif.). “Why would he cede this ground to her? It boggles my mind.” Even some of Sanders’ longtime allies were critical of the decision. Charles Chamberlain, chair of the liberal group Democracy for America, which endorsed Sanders’ 2016 bid, called Sanders’ absence a “missed opportunity.” “He could have shown how he’s learned and how he’s grown,” Chamberlain said. “A lot of people that had problems with him last time need to see that he’s changed.”

In order to become conversant on the issues of race, you have to be able to engage the people who are leading that conversation. Natalia Salgado, Center for Popular Democracy

Notwithstanding his challenges winning over African American voters in the 2016 cycle, Sanders has a dedicated and diverse grassroots following. He is fond of noting that in the 2016 primaries, he won more votes from young people of color ― African Americans, Latinos and Asians ― than Hillary Clinton and Donald Trump combined. In the intervening years, Sanders has stumped for a number of prominent candidates of color locked in tight races ― albeit generally only contenders aligned with his staunchly progressive ideology. Among others, he hit the trail for Florida gubernatorial candidate Andrew Gillum, Minnesota attorney general Keith Ellison, Michigan gubernatorial candidate Abdul El-Sayed, Chicago Rep. Jesús “Chuy” Garcia, and Atlanta mayoral candidate Vincent Fort. The Vermont senator has been equally dogged in his cultivation of relationships with black social justice leaders. He invited Catherine Flowers, an anti-poverty activist who works in predominantly black parts of rural Alabama, to speak at a live-streamed town hall on economic inequality in March 2018. In April 2018, he co-hosted an anti-poverty forum and rally alongside black activist leader Rev. William Barber, a founder of the Poor People’s Campaign, and spoke at Barber’s presidential candidate forum this past June. Whether due to that kind of outreach, or sheer name recognition, Sanders’ support among African American Democrats appears to have grown since his first run. A Morning Consult poll released earlier this month showed him trailing only Biden among black Democratic primary voters, with 21% of African American Democrats saying they plan to vote for him. He has even picked up the endorsements of a number of black state lawmakers in South Carolina, an early primary state that was notoriously unwelcoming to him in 2016. But Sanders still struggles with some black and Latino activists and opinion leaders who see Warren as a more effective messenger for discussing the ways race intersects with barriers created by class and gender. Sanders elicited jeers while speaking at the She The People Summit in April, a conference in Houston devoted to elevating issues important to women of color. Asked how he planned to address the unique challenges posed by racial injustice, Sanders hearkened back to his participation in the civil rights movement as a college student. “I know I date myself a little bit here, but I actually was at the March on Washington with Dr. [Martin Luther] King back in 1963,” Sanders started. The remarks drew scattered groans from activists in the room. One person called out, “We know!”

ASSOCIATED PRESS/Chris O'Meara Sanders campaigns with then-Florida Democratic gubernatorial candidate Andrew Gillum in Tampa in August 2018.