Erika Shields was not your old-line, law-and-order police chief.

She came into office in Atlanta in 2017 promising to clean up the “mess we created in the judicial system in the ’80s and the ’90s” by arresting too many people, especially young black men. She imposed a “zero-chase policy” after high-speed pursuits ended in fatalities. She was the first openly gay chief in Atlanta, and the second woman to lead the department.

In recent weeks, she was praised for firing the officers who had pulled two college students from a car and used a Taser on them — and for walking into a sea of protesters against police violence to hear their complaints in person.

And after Atlanta officers fatally shot a man Friday night in a Wendy’s parking lot, she is out of a job.

With her voluntary resignation Saturday, she joined a long and growing line of progressive, reform-minded police chiefs who have stepped down or been fired, often after high-profile episodes of police violence.

The once-prestigious position of police chief might be the most precarious job in America right now. And even with nationwide protests clamoring for change after the killing of George Floyd in Minneapolis in May, the risks are particularly high for those whose mission is reform.

“You can do everything right and have one officer, one night, do something — and all of a sudden your career is upside down,” said Chuck Wexler, the director of the Police Executive Research Foundation.

The foundation is often retained to help find police chiefs for cities, including Philadelphia, Baltimore and now, Louisville, Kentucky, where the chief was fired this month after a shooting incident that left the owner of a popular barbecue stand dead. The chief, Steven Conrad, was already under fire after an EMT, Breonna Taylor, was killed in a no-knock police raid of her apartment in March.

Chiefs must perform a high-wire act of retaining the respect of their officers, aligning with elected officials and giving the community genuine input into policy and operations, Wexler said. Often, pleasing one side means displeasing another. And now chiefs are facing fundamental questions over not just how they police, but why.

Even before the current moment of reckoning, chiefs brought in to fix troubled departments often found themselves abruptly unemployed. Baltimore is on its fifth commissioner since the death of Freddie Gray in police custody in 2015.

Many chiefs have complained that they faced resistance from within the department’s ranks, lacked the power to remove bad officers or install their own leadership teams, and were abandoned by those who appointed them when the going got tough. Some have been shown the door after intense pressure by police unions, while others have been faulted for high-profile episodes that happened on their watch.

Garry McCarthy was respected in law enforcement circles for ushering in an era of modernization and experimentation as superintendent of the troubled Chicago Police Department. He was fired in 2015 by the mayor at the time, Rahm Emanuel, over his handling of the fatal shooting of Laquan McDonald. Though McCarthy had viewed video of the shooting days after the incident, it took more than a year and a court order for the video to be publicly released.

McCarthy has said he removed the officer who killed McDonald from the streets immediately but did not have the power to fire him.

In some cases, chiefs have been deemed ineffective at solving problems that long predate them.

In 2017, Anne Kirkpatrick was brought in to clean up the Oakland Police Department, which had been under federal oversight since 2003, and which the mayor compared to a “frat house.” She was the fourth leader of the department in seven months.

She was fired in February after a vote by the Oakland Police Commission, a civilian board, citing broken trust and failure to make enough progress in fulfilling the conditions for release from oversight. The mayor signed off on the firing, while praising Kirkpatrick for a decline in gun violence and shootings by officers.

Frank Straub, the former public safety director in Indianapolis and former chief of police in Spokane, Washington, said reformers brought in from outside do not expect to last long. “We’re brought in to shock the system,” he said. A model in which an outside chief stays for a few years and grooms a successor can work well, he said. But in Spokane, it ended badly.

Straub, now the director of the Center for Mass Violence Response Studies at the National Police Foundation, instituted the use of body cameras, revised the department’s use-of-force policy and required deescalation training for officers. He said the rank-and-file welcomed the opportunity to become more professional, but the department’s brass opposed him. He was unable to assemble his own command team or remove people from leadership positions, he said.

“In some cities the way the labor contracts are written, you have to promote from within,” he said. “What does that do? It just perpetuates the system that’s already in existence.”

When the mayor who appointed him was running for reelection, Straub said, he was forced out with the release of letters from high-ranking officers who said he was abusive. A federal judge called his dismissal “a hot mess,” but his wrongful termination suit was unsuccessful.

In retrospect, Straub said, he might have been more successful if he had moved at a slower pace. But protesters of police violence today are demanding immediate change. Officers accused of misconduct are being identified, disciplined and even charged with crimes more swiftly, and chiefs have not been spared from repercussions.

In Atlanta, Shields appears to have resigned on her own.

“Out of a deep and abiding love for this City and this department, I offered to step aside as police chief,” she said in a statement. “It is time for the city to move forward and build trust between law enforcement and the communities they serve.”