Bernie Sanders, as yet the only challenger in the Democratic primary to get any real traction against Hillary Clinton, recently hit something of a pothole in his campaign. It happened last weekend at Netroots Nation, the annual meeting of liberal activists and base voters.

During a panel, Sanders tried to give his basic stump speech, which heavily focuses on economics and education. He was repeatedly interrupted by Black Lives Matter protesters. The idea, presumably, was to get him to address questions of racism alone, particularly as it relates to police brutality.

This he did, pointing to the prejudice of the criminal justice system and other factors, but also by repeatedly circling back to his favored topics of better-paying jobs and cheaper education. To many of the protesters, it seemed he was evading the question. Worse, he was clearly irritated by the constant interruption; he talked over the chanting, and afterwards reportedly canceled planned meetings with the same activists.

This is an unfortunate turn of events. However, it is a good opportunity for Sanders to polish his campaign message. He certainly could use some work on his racial justice language and policy, but he is not wrong to focus major attention on economic issues. Economic justice is not an alternative to racial justice — it is a fundamental component of it.

Of course, that is not to say that racial justice is wholly contained within political economy alone. That also is clearly false. Black Americans (and Latinos and others) face a great many non-class barriers, from violent, racist police to practically universal implicit bias.

However, many activists have endorsed the opposite extreme, arguing that race and class are basically unrelated. Here's Jamelle Bouie:

For Black Lives Matter activists, this is almost an insult. To them, racism is orthogonal to class: They’re two different dimensions of disadvantage, and to improve the picture on one isn’t always to improve the picture for the other. [Slate]

If Bouie is correctly representing the protesters' view, then it can only be described as a gross error. "Orthogonal" (at right angles) typically means completely unrelated. But even if we grant a softer interpretation, thinking of class and race as loosely related, that is still to badly understate the case.

For class is not independent from racism, it is a major mechanism by which the racist system operates.

Of course, upwardly mobile or even wealthy blacks are still routinely victimized by the police, as the cases of Prince Jones, Sandra Bland, or Henry Louis Gates demonstrate. But there are staggering differences in the rates of victimization.

Consider the criminal justice system, a major focus of Black Lives Matter. One rough way to consider the bias of this set of institutions is by overall lifetime likelihood of imprisonment of men by educational attainment — reasonable proxies for the levels of oppression and income, respectively. A 2009 statistical comparison between two cohorts of men on this measure, one born from 1945-49, and another born from 1975-79, provides a window into how such rates changed, since the latter cohort came of age just as the incarceration rate was reaching its peak.

Over that time, the overall imprisonment risk for men with some college, either white or black, didn't change much, increasing from 0.4 to 1.2 percent, and from 5.3 to 6.6 percent, respectively. That is a large disparity to be sure, but the numbers are nothing compared to the staggering rates among black high school dropouts, which increased from 14.7 to 68 percent. (White dropouts went from 3.8 to 28 percent.) As Berkeley sociologist Loïc Wacquant points out, this implies that the class gap within race groups is larger than the gap between them. In the 1975-79 cohort, blacks are five times more likely to be imprisoned than whites overall, but black high school dropouts are 10 times more likely than blacks that have completed some college.

Again, there is much bald racial prejudice revealed here, but poverty is an equal if not greater factor. Being poor is a known factor in about every social ill. Blacks do commit more crime than whites on a per capita basis, but this is largely explained by a poverty rate that is nearly three times greater. Thus, poor neighborhoods suffer both a lot of crime and crushingly heavy policing. When they are arrested, poor people often can't afford bail, or to hire a decent attorney, leaving them defenseless before the incarceration machine.

Poverty means constant stress and exhaustion as people struggle to balance critical needs on a tight budget — and its disadvantage is transmitted through time. Family income is tightly correlated with children's test scores, chance of college attendance, and future class position. Money, quite simply, is power.

Hence, an economic agenda aimed at the bottom of the income ladder is simply an indispensable part of any racial justice policy portfolio. Bringing down unemployment would disproportionately help blacks. Abolishing poverty — such a policy would cost only about a quarter of what the nation spends on the military — would strike a heavy blow against white supremacy.

That brings me back to politics. Hillary Clinton did not attend the Netroots conference (she has skipped it every year since her disastrous appearance in 2007). Instead, two days later she came out with a carefully polished statement on Facebook, name-checking all the right slogans and calling for body cameras, alternatives to incarceration for minor crimes, early childhood education, and voting rights.

All good stuff! But it notably leaves out any sort of strong economic agenda. And that's a place where Sanders' economic populism could come in handy. Any sort of attack on unemployment and poverty would cost a lot of money — meaning more taxes on the rich. The oligarchs funding Clinton's campaign are probably fine with slogans and police reform, but they would most assuredly balk at Sanders' eye-watering tax hikes and trillion-dollar infrastructure plan. It's a perfect pressure point for a left-wing challenger.