BUFFALO — When video of Buffalo police officers shoving and then walking past a bleeding, unmoving protester went viral, former Buffalo police officer Cariol Horne thought back to 2006 when, she says, a white colleague choked a handcuffed black man.

Horne says she told him to stop, then yanked the bigger officer’s arm away. According to the Buffalo News, the colleague accused her of jumping on him while he struggled for control. No one filmed the moment; other officers were there, according to news reports, but none backed her story during an independent arbitration, and Horne was fired.

“I always say that if I had to do it again, I would,” she told The Washington Post.

In 2009, that same white officer rammed, one at a time, the heads of four handcuffed African American teenagers into a police car. He went to prison for the kind of violence Horne said she had tried to prevent, fueling her quest for redemption and a pension. She was still pressing that case last month as an anguished country wondered why, in Minneapolis, no one in uniform stepped in as another black man said, “I can’t breathe,” before dying in police custody.

The officers who stood by are charged with aiding and abetting the killing, and police departments are adding policies that spell out the obligation to stop a colleague’s violence, known as a “duty to intervene” — something Minneapolis just moved to make enforceable in court. But those who have worked for years to reform troubled departments say that policy is the easy part. Much harder, they say, is changing the cultures of intense loyalty and deference to fellow officers that can help abuses of power go unchecked and unreported.

After an officer-involved shooting in 2015 drew sustained protests, the Minneapolis police announced new rules: Use force only when all else fails, and jump in when a colleague crosses a line. But those guidelines didn’t help George Floyd. And the nationwide protests that have followed his death, rife with more official accounts undercut by videos of brutality, have surfaced what looks to many like further evidence of the roadblocks to real reform — including in Horne’s city.

First, the Buffalo police said a protester tripped there last week. Then video showed two officers pushing a 75-year-old man, one attempting to stop before a peer shoves him forward. Some in riot gear walk on, while others come to halt, staring. “Stay in the line,” someone orders, and state police render aid.

Horne has been lobbying for lawmakers to encourage and protect officers who intervene against colleagues, trying since 2016 to get Cariol’s Law, a statute she drafted with the help of attorneys, passed at the state and local levels. She also has been out protesting every day since Floyd was killed. It’s the kind of activism that for years now has pushed law enforcement officials nationwide to rethink their tactics, increase accountability with body cameras and confront racial bias.

But like many officers who have alleged misconduct by their peers — and like many black protesters extra-attuned to uneven policing — Horne is skeptical that things will change.

This week, the Buffalo Common Council called on the mayor’s administration to better instill and enforce the police department’s “duty to intervene” policy: “It does not seem at times it is being followed,” said Council President Darius G. Pridgen, according to the Buffalo News.

Horne’s allegations of wrongful firing in Buffalo have never been validated, although council members have raised questions over the years and this week asked the New York state attorney general to review her case. The attorney general’s office on Friday declined to comment.

The now-retired officer whom Horne accused could not be reached, and his former lawyers did not respond to requests for comment. He and several colleagues prevailed in a lawsuit filed by the man Horne says she was trying to protect, a suit that alleged battery and other misconduct.

Others charging law enforcement colleagues with abuse have obtained legal victories after suffering through what they call retaliation for breaching a “code of silence.”

In 2018, a court awarded Lorenzo Davis $2.8 million after he said he was fired from Chicago police’s civilian oversight board for refusing to back off findings that officers were not justified in shootings.

There are rewarding moments, Davis said, like when an officer walked up to him one day to thank him. But a legal fight over the payout is still unfolding, and he says he’s mostly discouraged by the atmosphere he sees.

Another police whistleblower in Chicago, Sgt. Isaac Lambert, says his lawsuit alleging similar retaliation remains in limbo and his concerns unheard amid talk about reform. Lambert contends he was demoted for not helping to cover up a colleague’s unjustified shooting of a disabled 18-year-old. Aided by video, the Chicago Police Board found it was an “objectively unreasonable” use of force. The colleague was suspended, and the city reached a $2.25 million settlement with the victim.

“Sometimes in my field, we lack integrity,” Lambert said. “I mean, you shouldn’t be afraid to do what’s right.”

The Chicago Police Department said it cannot comment on pending litigation, and the civilian oversight board did not respond. Asked whether they think anything is changing in Chicago police culture, Davis and Lambert both shook their heads.

Baltimore Police Commissioner Michael S. Harrison is more optimistic. He comes from New Orleans, where he was charged with overhauling a department plagued by incidents of excessive force, scandal and discrimination.

If police weren’t going to report one another’s wrongs, he decided, he needed them to avert catastrophe in the first place. He launched a training program in which officers learned to pounce on a hand raised to strike or stand up to someone their senior.

“The old culture that we’re trying to get away from,” Harrison said, is all about showing your loyalty to your colleagues “on the back end. And the goal is to reverse that and learn to display loyalty on the front end by working to prevent bad acts from ever happening.”

The department said citizen complaints dropped about 15 percent in a year.

About 170 people from law enforcement around the country, including Minneapolis, came to conferences on the program in 2018 and 2019, said Ervin Staub, a professor emeritus of psychology at the University of Massachusetts at Amherst who developed the training. Harrison said he has the program on his to-do list in Baltimore.

Baltimore, too, has a “duty to intervene” policy. But that’s a mandate by a department,” Harrison said. “What we’re working to do is create officers who are willing — willing, and not mandated — to intervene.”

Although criminal charges remain tough to bring against law enforcement, Michael J. Mata, president of the Dallas Police Association, says body cameras, dash video and social media have combined to make police much warier of standing by as misconduct unfolds.

“There’s a different officer now than there used to be when I first came on 25 years ago,” Mata said.

Asked about the clips of police violence that have gone viral in the past few weeks, he said bad officers should be fired but called them outliers. Dallas police had more than a million contacts with the public last year, he said. “Officers are human beings, and human beings are flawed.”

Top Trump administration officials have also backed the “bad apple” view of police misconduct, with Attorney General William P. Barr suggesting Sunday on CBS News’s “Face the Nation” that he is hesitant to open an investigation into potential broader issues underlying Floyd’s death in the Minneapolis Police Department.

“I don’t think that the law enforcement system is systemically racist,” Barr said.

Lawyers for two of the fired police officers charged with aiding and abetting Floyd’s death have called their clients rookies following a veteran’s lead, echoing a common concern that younger officers may feel less comfortable interceding against excessive force. Speaking Monday night on CNN, attorney Earl Gray at first compared former officer Thomas Lane to the bystanders who cried out and filmed as Floyd was pinned.

“If the public is there and they’re so in an uproar about this, they didn’t intercede either,” Gray said. Lane at one point told his more senior colleague that he was “worried about excited delirium,” according to a criminal complaint.

CNN host Chris Cuomo pushed back: “The idea that the civilians should have rushed into a policing situation … don’t you think that’s asking a little too much of civilians and a little too little of your client?”

Black officers may shoulder an outsize burden in taking that potentially daunting step to intervene, some police officers say. Terrance Hopkins, who leads the Black Police Association of Greater Dallas, said he has observed a “race-driven dividing line” in moves to correct other officers, even as he believes most Dallas police officers are comfortable speaking up.

Several times, Hopkins said, he’s pulled other officers back when he sees them starting to get angry at a suspect.

“We would alert on it a lot sooner than most white people,” he said of the moments when police need to stop police to protect a member of the public. “Just because your skin is this color, you haven’t had to go through this type of behavior, that treatment.”

It might just be a tap on the shoulder, he said. “Hey. Step back. Let me handle it.”

Or it could be more forceful. Online, people roared with approval as video circulated of Krystal Smith, a black Fort Lauderdale, Fla., officer, berating a white colleague who shoved a kneeling protester.

“Yes! Yes!” someone yelled as Smith chased the other officer away, pointing a finger at him in outrage.

It was “an example of what men and women should do when they wear that badge,” said her police chief, Rick Maglione. The other officer was suspended.

In Buffalo last weekend, a very different scene took shape. Horne was driving home from a radio interview Saturday morning when someone alerted her to a large rally outside the courthouse for the two officers charged for pushing the protester. Fellow officers and other supporters blocked a news camera with an umbrella and cheered as the men left court, while the police union leader decried “a politically motivated witch hunt” to the Buffalo News.

Horne headed over, curious to see who was there.

If police “are going to back out when you have an officer stop police brutality, and they step up when you have officers knocking over 75-year-old men, then we have a big problem in Buffalo, New York,” she said.

Full of adrenaline and standing at the edge of the group with a bullhorn, she filmed as the officers’ supporters called her “liar” and jeered.

Felicia Sonmez contributed to this report.