“To some extent, and with respect to my white liberal friends in the white liberal base, these are people for whom politics is a deeply-held ideological passion,” he said. “The groups of people who have the most at stake – African Americans, Hispanics, LGBT – are much for serious for Hillary. They have got to be serious. White liberals get a psychic income for supporting Bernie Sanders, but they won’t suffer much if a Republican becomes president.”

Since the Netroots conference, Sanders has worked #BlackLivesMatter rhetoric into his speeches, and reached out to activists. But according the most recent Washington Post/ABC News poll, non-white Democratic voters give Hillary Clinton a net favorable rating of 77 points. Sanders’ net rating is just 19 points. Some of that is a function of Sanders lower name ID, but 23 percent of non-white voters view Sanders negatively – and only 9 percent view Clinton that way.

Sanders’ supporters, who number among the most intense partisans in the primary, have not helped close the gap. From the start of the Netroots interruption, some of them have chastised activists for making a loud, risk-free protest against a politician who should be their ally. David Atkins, a political strategist who was in the room for the interruption, went on a tweetstorm about how the activists had discredited the movement.