Many reasons have been put forward for why the left should participate in Bernie Sanders’ bid for the Democratic Party presidential nomination: he can win, his candidacy can pull the political debate to the left, it’s a chance to talk socialism with millions of Americans, it can build left organization and capacity.

Supporters of Sanders on the left (who I define as explicit anti-capitalists) think there’s no real downside to his campaign. But many others who find Sanders’ positions generally refreshing, myself included, point out that in the end Sanders will herd movements into a Democratic Party beholden to Wall Street. It’s hard to dispute this as he says he will support the eventual nominee, which will almost certainly be Hillary Clinton. Even if leftists who back Sanders sit out the general election that is of no consequence as they will have built a base of support that will be put to work for Clinton.

But there is another danger from Sanders’ campaign as a Democrat. Far from building movements, it can fracture them.

Exhibit A is Sanders’ response at the recent Netroots Nation conference to Black Lives Matter activists who demanded he speak about structural racism. After saying “Black Lives of course matter,” Sanders segued to income inequality. One protester retorted, “A class analysis does not take the place of a racial analysis.” When the moderator asked him about white supremacy, Sanders offered grim facts about Black life in America and said he’d “create millions of decent-paying jobs … make tuition at public colleges free [and] reform our trade policy.” One woman responded, “Jobs and college don’t stop the police from killing me. Trade policy doesn’t keep the police from killing me.”

Sanders blew it, but to his credit he has since changed his tune. He is the first candidate to discuss the death of Sandra Bland. Sanders also dropped the flawed idea of community policing and calls for addressing mass incarceration, mandatory minimum sentences, drug policy, the militarization of police, and use-of-force policy.

That might be the end of the story except it caused lingering divisiveness. Some Sanders supporters recognize he has a blind spot with race. Others circled the wagons, arguing Sanders should get a pass because he was a SNCC organizer in the 1960s. But politics is not like being a rock star where your fans adore you for old hits like marching with Dr. King or hanging with the Sandinistas. Politics is about what you will do, and that’s what Sanders failed to address at Netroots Nation.

A more substantive argument was put forward by Seth Ackerman, who argued that “Bernie Sanders’ signature issues aren’t ‘white’ issues” because the number one concern among people of color, according to polling data, is economic issues championed by Sanders. A week later Matt Bruenig advanced the same point. (After Netroots Nation, Ackerman doubled down and Bruenig stuck to his same argument.)

It is tempting to use class as an umbrella covering race because it is simpler to say Wall Street is the root of all evil. Nonetheless, most leftists understand economism is as much of a dead end as identity politics. Decent-paying jobs and free public education would not have saved Tamir Rice, John Crawford, Sandra Bland, and countless others obliterated by a society that defines their existence as a threat.

Economic reductionism is also ill thought out. It cannot explain why the white working class is so invested in whiteness. It does not indicate how to unravel the intertwined material, psychological, and cultural phenomena of structural racism. It revives discredited ideas, such as the Communist Party’s short-lived position in 1919 that the “racial oppression of the Negro is simply the expression of his economic bondage and oppression, each intensifying the other.” And it’s generally bad politics to tell a group of people, especially ones in a dynamic social movement, they don’t know their own history or community.

The fact the first real pushback from leftists against Black Lives Matter is around the 2016 election reveals how electoralism can induce activists to side with elites against the grassroots. Many Sanders supporters will be inclined to ignore if not defend every bad position he takes because they believe his campaign is a means to the greater end of advancing socialism.

Leaving aside Sanders is pushing for Keynesianism, not socialism or even social democracy, his campaign is antithetical to movement building. It’s top down, centered on one person, with no space for popular input to discuss his political failings, organization building, the limits of electoralism, or other strategies. After 2016 Sanders will not hand over his organization with its valuable lists and apparatus to the left. Past experience—Jesse Jackson’s Rainbow Coalition, Howard Dean’s Democracy for America, Barack Obama’s Organizing for Action—shows candidates keep control over their organization. Even Ralph Nader’s presidential bid in 2000 under the Green Party banner failed to benefit the Greens despite the 2.9 million votes he won.

Expecting a presidential campaign to solve the problem of organization is magical thinking. Leftists in Sanders campaign still need an existing organization to recruit for. As for talking socialism with the public, those options will be rare as campaigns tightly control volunteers, making them hew to talking points and scripts. It may make sense for union insurgents to back Sanders, but only because they’re working to reform pre-existing organizations, and their main target is labor leaders in bed with the Democrats.

Moreover, presidential campaigns create unresolvable conflicts. If Sanders endorsed reparations for African-Americans or admitted white supremacy exists, his rivals would demolish him. The more activists push him to acknowledge legitimate demands, the more defensive his supporters may become, hardening the divide. If anything, Black Lives Matter activists proved being outside Sanders’ campaign is more effective than being on the inside as they compelled him to address racial issues he had been ducking.

When he launched his campaign, Sanders said, “We must be vigorous in combatting terrorism and defeating ISIS.” Last year he backed Israel’s horrific war on Gaza, endorsing the continuation of the defining conflict in the most important geostrategic region in the world. In his announcement, Sanders ignored criminal justice and immigration reform. His communications director shrugged it off as you “can’t talk about everything in every speech.” His issues page is silent about the Pentagon’s budget, drone wars, Islamophobia, and the “war on terror.” There is a pattern of sidelining every issue around race, and his supporters tend to stay silent as one group after another is thrown under the campaign bus.

If America is the land of the get-rich-quick scheme, the American left is the province of the get-power-quick scheme. It’s always looking for the one tactic, the one protest, the one election that will change everything. Building power that’s strong and flexible takes years in the trenches developing organization, trust, community, leadership, action, and theory. Taking an electoral shortcut to power means fracturing movements as those with the least power are pushed to the sidelines. Leftists may thrill at finding a “socialist” horse on the electoral merry-go-round, but if they hop on board they’ll be the ones taken for a ride.