Editor's Note: (Julian Zelizer is a history and public affairs professor at Princeton University and the author of "The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society." He's also the co-host of the "Politics & Polls" podcast. The opinions expressed in this commentary are his own.)
(CNN) In the spring of 1991, one man holding a small Sony camcorder captured video that seemed to prove exactly what African-Americans had been protesting throughout the 20th century.
Millions watched their television screens as four white Los Angeles police officers viciously beat a 25-year-old African-American man named Rodney King, over and over again.
The video promised to be transformative. Civil rights leaders hoped that the power of those images would be enough to change the way that race influences the US criminal justice system.
But they were wrong.
The officers were acquitted in April 1992 by an jury in California's conservative Simi County, where the trial had been moved in an effort to diminish bias.
Furious about the trial's outcome, massive riots broke out in South Central Los Angeles. More than 50 people were killed, over 2,000 injured and hundreds of buildings were burned.
Amid the violence, King spoke to reporters asking for people to "get along."
To many South Central residents, the verdict meant that even visual proof of police brutality against African-Americans did not matter.
The Rodney King video -- which today we would say went "viral" -- circulated with the kind of speed that nobody had seen before. As one media critic recalled at the time of King's arrest in 1991, "the internet was barely more than a curiosity at colleges ... Cell phones were the size of concrete bricks, and nearly as heavy. Video-sharing websites, portable telephones with cameras and digital video were still mostly dreams in science fiction stories."
Throughout the 20th century, African-Americans had protested the way that they were systematically harassed by police. Police harassment and violence had been the trigger for many of the riots that rocked American cities, including the devastating unrest in Newark, New Jersey; and Detroit some 50 years ago.
The federal government finally acknowledged these problems in the Kerner Commission report of 1968, which placed race and policing front and center -- though the conservative turn in politics meant that no concrete steps were taken to put an end to these conditions.
Before the Rodney King video, Americans had seen images of police attacking African-Americans, but those images had primarily been from grassroots civil rights protests such as Birmingham in 1963 and Selma in 1965, or in the pictures and footage from urban riots.
Rarely had they seen such graphic evidence of what many in the black community described as the routine violence at the hands of police.
The Rodney King video and its outcome were part of the reason so many African-Americans polled were willing to believe in October 1995 that the Los Angeles police had framed O.J. Simpson -- a position that didn't make sense to many white Americans.
This had less to do with the former football star himself than with the underlying problems exposed with King.
The Rodney King images launched a national debate that has continued through this day about race and policing. In recent years, smartphones have allowed ordinary citizens to capture incidents in places like Staten Island, St. Paul and Baton Rouge, where African-American men were killed by police.
The problem is that these graphic images don't necessarily produce substantive reforms. Racism runs much more deeply in the body politic than any photograph or any image can overcome.
The continued emphasis in American politics on "law and order" rather than "criminal justice reform" means that transforming criminal justice institutions is difficult. The localistic structure of our criminal justice system prevents national solutions to racism from being easily undertaken.
Police authorities also command immense power and prestige, as well as union organization, making it difficult to obtain punitive action when officers abuse their power.
Although we are a long way from the Jim Crow era, racism also remains a powerful force in the American psyche that limits our collective willingness to move forward with substantive reform.
African-Americans, as well as Latinos, continued to experience daily harassment -- and sometimes deadly violence -- from police based on assumptions and biases about race, rather than good policing.
As CNN revisits the impact of the Rodney King beating as part of "The Nineties" series, it's an occasion to renew the vigorous debates that emerged in the final years of President Obama's time in office when Black Lives Matter activists pushed these questions front and center, building on the outrage sparked by the videotaped police killings of Eric Garner, Philando Castile and Alton Sterling.
It is vital that in 2017 we don't make the mistake that we did in 1991, or in 1968, and that we keep trying to build bipartisan support for federal and state responses to prevent the kind of racism that still exists within the very institutions that should be at the forefront of protecting the rights and security of all Americans.