Demonstrators march through downtown Chicago this past weekend. A video showing the shooting of teenager Laquan McDonald by Chicago Police officer Jason Van Dyke has brought calls for the ouster of Mayor Rahm Emanuel. (Scott Olson/Getty Images)

In Chicago, Mayor Rahm Emanuel fired his police chief and faces a growing clamor for his resignation.

In Baltimore, Mayor Stephanie Rawlings-Blake fired her police chief and abandoned plans to seek reelection.

And in San Francisco, protesters are demanding the head of yet another police chief, prompting Mayor Edwin Lee to vow last week to overhaul police procedures regarding deadly force.

“Black lives do matter,” Lee (D) assured reporters.

Across the nation, protesters are no longer satisfied with in­dictments or special prosecutors when evidence emerges that someone has died unnecessarily at the hands of police. Instead, they have been seeking — and increasingly securing — the ouster of top officials, as well as concrete steps toward real reform and accountability.

“In my lifetime, I haven’t experienced a moment like this,” said Craig Futterman, a law professor at the University of Chicago who founded the school’s Civil Rights and Police Accountability Clinic. “I’m usually more of a cynic and a skeptic, but this feels different.”

Activists and criminal-justice experts say the national ethos regarding race and policing has changed dramatically since a black teenager was shot to death by a white police officer in Ferguson, Mo., in August 2014. Since then, sustained protests in multiple cities, an aggressive social media campaign and a steady drip of viral videos revealing questionable police shootings have eroded the societal reflex to defend police and blame the dead victim.

The videos have also soured the public’s opinion of law enforcement.

In June, a Gallup poll found that about half of Americans surveyed expressed “a great deal” or “quite a lot” of confidence in police, a 22-year low. Meanwhile, a separate poll found the percentage of black Americans who see race as the nation’s most urgent problem increased from 3 percent at the beginning of 2014 to 15 percent after Ferguson.

“The American public has accepted that this is a real problem. They’ve seen Eric Garner, then Michael Brown, then Walter Scott, then Sandra Bland,” said Al Sharpton, the New York-based activist who for decades has been among the nation’s most prominent proponents of policing reform.

“We’ve seen a shift because, with story after story, the public says, ‘Wait a minute. They can’t be making all of this up.’ ”

That shift has prompted law enforcement officials to undertake a genuine reexamination of the way American police do business. A presidential task force and the Police Executive Research Forum, a law enforcement think tank, have urged police officials to rethink training so that officers can learn to avoid the use of deadly force.

An evolving movement

The protest movement is also evolving. Campaign Zero, a policy-focused branch of the Black Lives Matter movement, released a review of police union contracts earlier this month, highlighting clauses that they found problematic. Among them: In many cities, officers have the right to refuse to talk to investigators for 48 hours after a shooting and to strike embarrassing information from their personnel files.

All this has occurred alongside an uptick in criminal charges against officers who kill or otherwise break the law.

So far this year, police have shot and killed more than 920 people, according to a Washington Post database tracking such shootings.

Eight officers have been charged, slightly more than the annual average over the past decade, according to a Post analysis.

In a 24-hour span last week, four officers were indicted in connection with three different fatal police shootings, including the death of 6-year-old Jeremy Mardis last month in Marksville, La.

Meanwhile last week, former Oklahoma City police officer Daniel Holtzclaw was convicted of raping as many as 13 women he encountered while on patrol, all of them African Americans. He faces up to 260 years in jail.

Among the most heartening developments, many activists say, has been a subtle shift in the public reaction to questionable police shootings. Instead of getting stuck on minute physical details or the shooting victim’s criminal record, public officials and the media now tend to focus on the bigger picture, especially when there is video evidence.

Most recently was the shooting Saturday morning of Nicholas Robertson by Los Angeles County sheriff’s deputies — captured by a bystander in a video that appears to show the man walking and then crawling away as police open fire.

The video almost immediately sparked national outrage, and calls for the officers involved to be fired and charged with murder. Officials with the Los Angeles County Sheriff’s Department — which has been responsible for at least 12 fatal on-duty shootings to date, according to the Post’s database — has said Robertson had a gun when he was shot and has vowed a full investigation into the shooting.

Condemnation was equally swift in San Francisco after horrified bystanders posted cellphone videos of police shooting Mario Woods on Dec. 2.

Woods, 26, suffered from mental illness, had an extensive criminal record and had spent most of his adult life in prison. But none of that seemed to matter in the face of the videos, which show Woods against a wall, hands at his sides, surrounded by officers with guns drawn. He appears to be trying to escape — arms still at his sides — when the officers open fire.

The videos depict a shooting that appears to be two things at once: probably legally justified, because police said Woods was holding a kitchen knife and refused to drop it, but also probably preventable, because Woods clearly was not on the attack.

The public conversation in San Francisco quickly came to focus on the second point. Unlike in Ferguson, where officials refused to consider that Michael Brown’s death may have been a symptom of a wider problem in policing, San Francisco Police Chief Greg Suhr immediately called for his officers to be equipped with less-than-lethal weapons, such as stun guns, even as he defended their actions.

Lee, too, promised reforms to make lethal force a “last resort.” And top officials on the San Francisco Board of Supervisors issued a statement calling the Woods case a “tragedy” that highlights the fact “that police procedures themselves can seem to encourage violence.”

In Chicago, protesters are probing more deeply into issues of transparency, accountability and trust, blaming Emanuel (D) for the city’s decision to wait more than a year before releasing police dashboard-camera video of the shooting of Laquan McDonald, 17. McDonald was also armed with a knife, and he was moving away from police when Officer Jason Van Dyke shot him 16 times in October 2014.

Van Dyke’s attorney has said the officer was in fear for his life and following departmental guidelines when he opened fire. But prosecutors charged him with murder on the day the video was released.

A mayor’s apology

Last week, Emanuel offered an emotional apology, calling McDonald’s death “totally avoidable.” In addition to firing the police chief, Emanuel has vowed to create a police accountability task force and to end the police department’s notorious “code of silence” — though none of it has quelled calls for his ouster.

There is no video of an un­secured Freddie Gray, 25, suffering fatal injuries in the back of a Baltimore police transport van in April. But months after her city erupted in riots, Rawlings-Blake (D) abruptly decided in September to cancel her reelection plans rather than inject campaign politics into the city’s recovery. A jury is set to begin deliberations Monday on the fate of the first of six officers charged in connection with Gray’s death.

“The last thing I want is for every one of the decisions that I make moving forward — at a time when the city needs me the most — to be questioned in the context of a political campaign,” Rawlings-Blake said at a surprise news conference days before the scheduled announcement of her reelection bid.

Other elected officials have also taken note of the changing mood. New York City Mayor Bill de Blasio (D) was elected in 2013, in part for his promise to end “stop and frisk” tactics. New York Gov. Andrew Cuomo (D) earlier this year signed an executive order requiring special prosecutors to review the cases of any deaths at the hands of police officers. And California Attorney General Kamala Harris (D) has published a searchable database of a decade’s worth of police-shooting data.

This has been a year, Sharpton said, “in which we got Cuomo to agree to special prosecutors, a year when we got cameras on cops in dozens of cities, a year when the [U.S. Justice Department] launched investigations into major city departments.”

If protesters succeed in toppling Emanuel, Sharpton said, “that would be the crowning of a huge win for this wave of activism.”