PHOENIX — Two major poles of the modern progressive movement — the racial justice movement and the economic reform wing — crashed into each other this weekend in Phoenix at Netroots Nation, an annual conference for liberal activists. Neither group left the encounter feeling satisfied.

The confrontation took place when activists from the racial justice group Black Lives Matter crashed a Saturday town hall featuring Bernie Sanders, a Democratic presidential candidate and beloved figure of progressives.

The protesters demanded that Sanders, along with fellow candidate and town hall attendee Martin O’Malley, explain what they would do to stop police violence against unarmed black people. “What will you do to stop police unions from battering our names after law enforcement kills us? I want to hear concrete actions,” said Black Lives Matter co-founder Patrice Cullors, who took the stage during O’Malley’s scheduled appearance.

Sanders made little effort to disguise his irritation, telling the audience, “If you don’t want me to be here, it’s OK.” Shouting over the chants from the protesters, he plowed ahead with some prepared remarks on wealth inequality.

That response earned him loud boos and criticism from many of those sympathetic to Black Lives Matter. MoveOn.org’s executive director, Anna Galland, said in a statement after the town hall that “the implication that solutions to economic inequality will take care of racism represents a fundamental misunderstanding of how race operates in our country.”

That is troubling news for Sanders, whose campaign is built around the premise that the majority of Americans agree that the central political question in the U.S. is how to remedy the widening gap between the rich and everyone else.

He told The New York Times earlier this month that he believes working people of all backgrounds and ideological persuasions “are profoundly disgusted with the state of the economy and the fact that the middle class is being destroyed and income going to the top 1 percent.”

He is calculating that he can win white and nonwhite working-class voters by focusing narrowly on economic issues and only footnoting racial justice concerns. In other words, Sanders is running for president as a social democrat and gambling that the conditions for building social democracy exist in the United States. His experience at Netroots Nation shows why such a gambit is a long shot.

Sanders, a democratic socialist, has long identified himself with the politics of European social democratic parties, particularly those in the Nordic states. Last year he told Fox News that the U.S. has “a lot to learn from democratic socialist governments that have existed in countries like Denmark, Sweden, Finland [and] Norway, where all people have health care as a right, where higher education is free, where they have a strong child care program [and] where they don’t have the massive type of wealth and income inequality that we have in the United States of America.”

Those countries — particularly Denmark, Sweden and Norway, the three Scandinavian nations — are model social democratic states. In the years after World War II, the Scandinavian nations were governed by quasi-socialist political coalitions that sought not to eradicate capitalism but to tame it.

To do that, social democratic parties typically relied on cross-class constituencies, held together by a shared belief that the state should protect and provide for the most vulnerable in society. Sanders seems to want to build the same type of coalition in the U.S.

During a Saturday campaign rally at the Phoenix Convention Center, he told a crowd of more than 11,000 supporters that he wants to be part of a mass “political revolution” that transcends regional, racial and ideological boundaries.