Hillary Clinton gave a sweeping speech on race in Harlem on Tuesday, making a broad and sometimes emotional pitch for Democrats and all Americans to take the threat of systemic racism seriously.

Clinton's speech touched on many topics about race. She discussed mass incarceration. She unveiled her plan to undo the school-to-prison pipeline. She called on the country to help her end segregation in schools.

But there was a particularly powerful moment in which Clinton called on all Americans, white included, and particularly Democrats to help eliminate systemic racism. She said:

We Democrats have a special obligation. If we're serious about our commitment to the poor, to those who need some help, including African Americans, if we continue to ask black people to vote for us, we cannot minimize the realities of the lives they lead or take their concerns for granted. You know, you can't just show up at election time and say the right things and think that's enough. We can't start building relationships a few weeks before a vote. We have to demonstrate a sustained commitment to building opportunity, creating prosperity, and righting wrongs — not just every two or four years, not just when the cameras are on and people are watching, but every single day. So here's what I ask of you: Hold me accountable. Hold every candidate accountable. What we say matters, but what we do matters more. And you deserve leaders who will do whatever it takes to tear down all the barriers holding you back and then replace them with those ladders of opportunity that every American deserves to have. I'm also asking all Americans to join in that effort. As Cornell Brooks, the new head of the NAACP, said in our meeting this morning, none of this is a "they" problem; it's a "we" problem. And all of us have to admit that. And you know what? It is not an urban problem. It's an American problem. Ending systemic racism requires contributions from all of us, especially those of us who haven't experienced it ourselves.

To some extent, Clinton's speech is responding to a growing issue for the Democratic coalition: racial justice. For one, she is trying to shore up support from black voters in South Carolina, one of the next states to vote in the Democratic primary. But it's also true that the importance of these issues has grown over the past couple years thanks to the Black Lives Matter movement — and that indicates a broad shift in US politics.

Black Lives Matter has forced Democrats to talk about racial justice

Very early in the Democratic race, it wasn't clear if criminal justice issues would play a major role. Besides Clinton, whose first big campaign speech hit on criminal justice and race, the candidates didn't seem to talk about racial justice much.

This changed quickly: Pretty soon, Black Lives Matter protesters began showing up at rallies for Bernie Sanders and ex-candidate Martin O'Malley and demanding that the candidates talk about these issues. So the candidates released racial justice platforms.

But the Democratic candidates weren't just responding to some heckling at rallies — they were also responding to a clear shift in American politics, one that's visible in the polls.

A 2015 survey from Gallup, for example, found that Americans are more likely to say black people are unfairly treated in all aspects of society, including police encounters. And a survey from the Pew Research Center found a 20-year high in Americans saying racism is a "big problem."

But these general findings don't show the partisan divide on this issue. When divided by party, Pew found 61 percent of Democrats, including 61 percent of self-identified conservative and moderate Democrats, said racism is a big problem. By contrast, 41 percent of Republicans said it's a big problem — a 20-point gap. (One caveat: Many white Americans, which make up the great majority of the Republican Party, say racism against white people is worse than bias against black people.)

Looking at these polls, it's hard to think of anything besides Black Lives Matter and the media coverage surrounding it — of mass incarceration, police use of force, and so on — that drove the shift. And Democrats, seeing the interest in their base, have gone to great lengths to capture that shift in their campaigns — hence Clinton's speech.

Why Democrats need to talk about racial justice

The broader context here is not just that Democrats are paying attention to a growing issue in their coalition of voters, but that Democrats are finally participating in a long-running conversation that has been left to the right for years.

As white supremacy and systemic racism lost support among much of the public, the Republican Party and conservatives did not simply drop the issues and move on. They instead adopted dog whistles and coded language that continue in much of public dialogue in America today. It was a crucial part of Republicans' Southern strategy following the 1960s — by invoking many white Americans' racial resentments, GOP presidential candidates successfully secured states in the South that historically went Democrat.

Ian Haney-López, author of Dog Whistle Politics: How Coded Racial Appeals Have Reinvented Racism and Wrecked the Middle Class, recently laid out how this worked.

"The 20th century witnessed a strong push to get beyond white supremacy, to get beyond a social commitment to ideas that elevate whites as human and decent and worthy and nonwhites as less than human and dangerous and unworthy of concern," Haney-López told me. "That push has been most successful at a formal level, but what you see in response sort of as an evolution is the search for proxy language that allows you to express the same fears in ways that aren't formally offensive."

Today, many conversations about policy on the right are rooted in this kind of racial anxiety. With criminal justice and public safety, many white people hold implicit (and sometimes explicit) biases against black people, often characterizing black men in particular as criminals. With immigration, there are fears about Hispanic and especially Mexican immigrants changing the makeup of America. With national security, much of the conversation is really an expression of Islamophobia.

The rise of Donald Trump demonstrates this: Many Republican voters back a platform that is racist, nativist, and xenophobic. Trump launched his campaign characterizing Mexican immigrants as rapists and criminals. He explicitly supports banning a whole group of people (Muslims) from entering the US. And Trump supporters back their candidate proudly, despite attempts by elites in the party to take down Trump.

Democrats basically let this kind of conversation and language persist on the right without much interference for decades. It dominated the US's criminal justice conversation for much of the 1980s and 1990s — Clinton herself talked about "superpredators," a word that has been repeatedly used by politicians used to invoke white Americans' fear of black crime.

This type of language had serious consequences: It's one of the reasons that tough-on-crime measures, the drug war, and mass incarceration have been allowed to go on for so long, despite warnings from black leaders that this was having a horrific impact on minority communities.

"Almost every conversation on the right has as a subtext an indication of race," Haney-López said. "On the left, we've got this move that says we shouldn't talk about race, because race is divisive, so let's just focus on economics. It's a disaster, because we're not responding to the racial narrative, so we're not responding to white people's genuine racial fears. At the same time, we're not really addressing the genuine racial justice issues confronting communities of color, which is part of what the Black Lives Matter movement is trying to do."

Clinton's speech shows this is changing. Democrats aren't just talking more about this issue — they're making major speeches about it.