Many reasons have been put forward for why the left should be involved in Bernie Sanders’ bid for the Democratic Party presidential nomination: he can win, his candidacy can pull the party or at least 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 (which I define as explicit anti-capitalists) think there is no real downside to his campaign. Now, many find Sanders’ positions generally refreshing, myself included, but that’s not enough. The real issue for the left is what role does his campaign play in organizing, and it’s indisputable that Sanders will herd movements into a Democratic Party beholden to Wall Street interests. Sanders makes no bones about this, saying 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 served their purpose of building 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 to Black Lives Matter activists who confronted him at the Netroots Nation conference on July 18. Protesters wanted him to speak about structural racism, but Sanders kept pivoting to economic issues. After saying “Black Lives of course matter,” Sanders segued to income inequality, which provoked one audience member to retort, “A class analysis does not take the place of a racial analysis.” When the moderator asked him about white supremacy, Sanders offered some grim facts about Black life in America and said he would “create millions of decent-paying jobs … make tuition at public colleges free [and] reform our trade policy.” As he spoke a woman responded, “Jobs and college don’t stop the police from killing me. Trade policy doesn’t keep the police from killing me.”

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