President Biden has come a long way since his “Lock the SOBs up” days, pledging on the campaign trail to cut incarceration by 50 percent — and even “go further.” Such a proposition would need support in all 50 states, because the federal government oversees only about 10 percent of the 2.1 million Americans who are behind bars. And that presents a huge obstacle to the president’s ambitious goal: Research shows that many White Americans see incarceration as a “Black problem,” and the more they see it that way, the less willing they are to do anything about it.

Biden and others might surmount this resistance, however, by highlighting a surprising trend: White Americans have been filling jails and prisons at increasing rates in the 21st century. Reducing incarceration, reformers can credibly argue, will benefit Whites as much as Blacks.

It’s true that the criminal justice system is suffused with racial biases that harm African Americans and Hispanics while favoring Whites. But consider some data, beginning with jails. Jails are operated mainly by cities and counties and generally hold inmates for less than a year. Data from the U.S. Bureau of Justice Statistics shows that since 2000, the rate of being jailed increased 41 percent among Whites while declining 22 percent among African Americans. Beginning in 2017, the White rate of being jailed surpassed that of Hispanics for the first time in living memory. And in 2018, Whites became 50 percent of the jail population, particularly notable because Whites represent a lower proportion of the U.S. population than they have in centuries.

Prisons, operated by states and the federal government, hold individuals who have committed more serious crimes. Unlike jails, their overall population has been shrinking, but parallel racial dynamics are evident. The White rate of imprisonment is down only 12 percent in this century, whereas the Hispanic rate has fallen 18 percent and the Black rate is down a remarkable 40 percent. The trend of African Americans leaving prison is accelerating, dropping Black imprisonment rates to levels not seen in 30 years. The causes are still debated, but the collapse in urban crime most likely played a role.

These changes coexist with continuing, pervasive discrimination against African Americans in the criminal justice system and huge disparities in incarceration. Blacks, for example, are five times more likely to be imprisoned than Whites. Race-based critiques of mass incarceration remain essential, and the Black Lives Matter movement has proved that millions of diverse Americans respond to them. At the same time, the increasing share of Whites among inmates gives opponents of mass incarceration a chance to expand their reach and impact. Like it or not (and we don’t), ample evidence shows that many White Americans are more likely to respond compassionately to a social problem once they appreciate its adverse impact on Whites.

The opioid epidemic illustrates the phenomenon. When crack cocaine afflicted Black communities in the 1980s, the national response was far more punitive than it has been to the current opioid problem. The proportion of state prisoners who were sentenced for drug crimes more than tripled in the ’80s but has actually dropped over the course of the opioid epidemic, during which the Affordable Care Act greatly expanded access to addiction treatment. Fear of street violence may have played a role: Crack dealers carried guns, whereas Purdue Pharma executives dealt death in more genteel ways. But race mattered. The crack cocaine epidemic put Black faces on America’s televisions each night, whereas reports on the opioid epidemic show White faces, many from “good” suburban homes. White Americans began to see “someone like them” suffering, which psychological research suggests blunted their desire to punish.

Racial codings of social problems influence public attitudes through two basic processes. The first is in-group favoritism, which is greater appreciation of and empathy for people we perceive as similar to ourselves. Such favoritism increases willingness to help a stranger in distress, leave a big tip at a restaurant or grant a promotion at work, among many other kindnesses. In-group favoritism is not limited to race (we can be favorably disposed to someone over something as trivial as sharing a first name or a birthday), and people of all races are prone to it. But race is clearly one of the many dimensions by which we judge similarity, so that as more White Americans understand that more Whites are behind bars, they may feel increased compassion toward prisoners and voice more support for policies to reduce incarceration.

The other process in play is more disturbing, because it implies an active attempt to harm others. Sociologists Rachel Wetts and Robb Willer documented that, when told the income gap between White Americans and Black and Latino Americans was shrinking, Whites favored social welfare programs that they believed particularly helped other Whites. But they became less supportive of programs that they thought particularly helped minorities. Wetts and Willer concluded that perceived threats to the racial hierarchy drive White opposition to helping Black Americans. The same Whites who recoiled at a Black man rising to the presidency, for example, might oppose prison reforms (shorter sentences, better health care, early release for the sick and elderly) precisely because they believe that the beneficiaries will mainly be Black. Informing such people that prisoners are increasingly White could soften their hostility.

Persuading people to join the fight against mass incarceration because Whites stand to benefit is bound to repulse those already committed to the cause. But because each state runs its own prison system and sets most criminal penalties, building a nationwide coalition is essential. That can happen only by shifting the opinion of people who are not moved by — or indeed are even comforted by — the thought of prison populations being mostly Black. And exploding the idea that mass incarceration is only a “Black problem” may allow us to reimagine a broad range of other issues, such as the policing that helps feed it.

When asked if Blacks suffered the most from racial injustice, James Baldwin replied, “No, we are only the ones who are dying fastest.” Baldwin wasn’t speaking specifically of mass incarceration, but he could have been. Mass incarceration is aimed at Black and Hispanic people, but hundreds of thousands of Whites have been imprisoned in a society that promotes locking people up. Highlighting the Whitening trend could help Americans appreciate how a furnace fed by racism eventually consumes us all.

In the effort to control Black and Brown people through the criminal justice system, White Americans have shown a stunning willingness to tolerate a huge number of White prisoners as collateral damage. And once such systems are built, they have a remarkable capacity for self-preservation; jail populations, for instance, have stayed constant even as crime has plummeted. So we cannot say how well a strategy drawing attention to the Whitening trend will work. In his book “Dying of Whiteness,” physician Jonathan Metzl argues that White people’s racial resentment can lead them to cut off their nose to spite their face — opposing policies that would help them because they would help Black citizens, too. Indeed, numerous economists have concluded that America’s long history of hostility toward Black people has left it the sole advanced economy without some form of universal health care. If some White Americans are willing to give up health care to keep their place in the racial hierarchy, perhaps they are willing to risk imprisonment as well. Yet the reversal in rhetoric during the opioid crisis shows that entrenched policies can be changed.

What’s more, in a remarkable moment of convergence, libertarians, religious leaders and racial-justice advocates oppose mass incarceration for separate but overlapping reasons. Were our country more just and less dismissive of Black pain, growing White incarceration would have no special weight in assessing the moral value of locking up more than 2 million of our fellow citizens. Opponents of mass incarceration — including Biden — should continue to denounce racism within the criminal justice system. But the president can also remind Americans that our racial fates are joined: All of us would benefit from the end of mass incarceration.