Throughout Bernie Sanders campaign, leftwing supporters have struggled to explain why the Vermont Senator doesn’t poll well among African Americans and Hispanics. Given that poverty so disproportionally affects ethnic minorities, shouldn’t these voters jump at the chance to elect a socialist candidate who aims to reduce economic inequality?

But just as Sanders’ socialism has made him an appealing candidate to many, it’s also part of his problem. He keeps answering questions about racism by referring to economic policies. These answers make sense to Sanders and his supporters, but they’re not helping him connect with these crucial voting blocks.

For example, when Sanders answered a question on race relations with comments about job creation, a legal analyst, Imani Gandy, pointed out that more jobs wouldn’t have made any difference to Sandra Bland.

For socialists, the debate about whether racism can be adequately addressed by economic reform is an old one. Socialism is distinct from but rooted in the ideas put forward by German philosopher Karl Marx in the 19th century. Marx believed that economic revolution would ultimately solve all societal injustices. He saw racial divides as false, and a means of separating the working class to prevent them from uniting and overthrowing the bourgeoisie.

“He thought racial differences couldn’t be salient under conditions of mass commiseration,” Amy Baehr, philosophy professor at Hofstra University, tells Quartz.

This idea is explicitly and controversially addressed in Marx’s “On the Jewish Question,” where Marx argues that, though Jews could obtain a lower form of “political emancipation” as Jews, religious and racial identities would have to be transcended before a higher form of “human emancipation” could be possible.

Meanwhile, on the question of gender inequality, Marx certainly believed that his economic policies would help women. But his writing was largely gender-blind, and he said very little about the specific forms of exploitation faced by woman.

Of course, socialism evolved beyond Marx’s ideas. (Today, it’s broadly used to describe policies that focus on enabling the more fortunate in society to share the burden suffered by the unlucky.) But among certain committed socialists, there remains a lingering resistance to specifically addressing racial and gender issues. When feminism emerged as a political theory movement in the 1960s, Baehr tells Quartz that there was considerable debate about whether it was possible to be a feminist Marxist.

And so while socialism certainly faces opposition from rightwing politicians, it can also be criticized by those on the left—particularly those who advocate identity politics.

Hillary Clinton’s political history is closely tied with this outlook. For several decades, the Democrat Party has been associated with identity politics and Clinton came of age politically during the late ‘60s and early ‘70s, at a time when the Party was embracing this view.

At this time, the Democrat Party became a coalition of various interest groups, loudly advocating for and welcoming African Americans, Latinos, Jews, and white ethnic minorities, among others. Though the makeup of groups has changed, this conglomeration has been central to the Party’s identity ever since. (In 1984, President Ronald Reagan explicitly pointed this out, saying, “Their government sees people only as members of groups. Ours serves all the people of America as individuals.”)

As such, voters deciding between Clinton and Sanders aren’t simply evaluating where each candidate lies along a linear political spectrum, but are deciding between two, fundamentally different, American leftwing traditions.

Of course there’s never any one, clear-cut reason for a politician’s success or lack thereof with any particular group. And Sanders has made attempts to address racism as a societal problem. But socialism’s history of framing racial injustice as an economic problem can certainly explain some of Sanders’ awkwardness over how to tackle racism.