Bill de Blasio ran for mayor as a progressive who promised to repair splintered relations between police and communities of color. It’s been an ongoing test for the mayor in his first 18 months in office, especially in the year since Eric Garner's death following a chokehold by a New York City police officer.

The mayor had pledged to end the misuse of stop-and-frisk policing and in his first month in office, he announced an agreement with the plaintiffs in the federal stop-and frisk-lawsuit, Floyd vs. City of New York. The city was dropping its appeal in the case, setting it on the path to reform; a federal judge had ruled that there was an unconstitutional use of the police tactic.

“We believe in our obligation, the most fundamental one that there is in government, to keep people safe,” de Blasio said as he announced the agreement at a recreation center in Brownsville, Brooklyn. The strategies that would do that successfully, he argued, did not unfairly target African American and Latino men.

But even as de Blasio was ushering out a police tactic that had defined the department under the previous administration, he still tapped a veteran law enforcement leader to be his Police Commissioner. It was move that raised eyebrows among some police reformers.

Commissioner Bill Bratton is considered one of the architects of broken windows policing — combating quality-of-life offenses as part of a larger crime reduction strategy. He and the mayor are committed to broken windows. But it was one such quality-of-life offense that lead to the enormous backlash against the police in the past year.

Eric Garner was an unarmed black man with a history of run-ins with the police. He was allegedly selling loose cigarettes along a commercial strip in Staten Island when he was approached by plainclothes officers.

A cell phone video captured what happened next. Garner refused to surrender. Daniel Pantaleo, a white police officer, attempted to bring him down by wrapping his arm around Garner’s neck. Garner’s plea, "I can't breathe," repeated 11 times, went ignored. He was pronounced dead at the hospital an hour later.

New York City was thrust into a national conversation about policing tactics, community and race. It also set de Blasio on a collision course with the very progressives who had elected him to bring about change.

After Garner's death, de Blasio held a round table discussion at City Hall on police and community relations. Bratton sat directly to his right and the Rev. Al Sharpton to his left. The optics of the scene were fodder for those critics who questioned whether de Blasio was equating the influence of his own police commissioner with Sharpton, who led a march across Staten Island against police brutality.

Sharpton had been a close ally to the mayor, but he did not hold back from sounding off about his concerns.

“The fact of the matter is, given the data that we are seeing in terms of these broken window kind of operations, it’s disproportionate in the black and Latino community,” said Sharpton.  He added, “If Dante wasn’t your son, he’d be a candidate for a chokehold.”

Months later, a Staten Island grand jury decided not to bring charges against Pantaleo. In response, the mayor spoke personally about the anxiety he and his wife feel about the safety of their biracial son, Dante.

“We’ve had to literally train him, as families have all over this city for decades, in how to take special care in any encounter he has with the police officers who are there to protect him,” de Blasio said at a church on Staten Island, where he was flanked by clergy and community leaders.

Those words may have comforted some, but they were seen as anti-cop by de Blasio's most fervent detractors.

Demonstrations erupted in cities all over the country in response to other deaths involving police officers. When marchers once again returned to the New York City streets, the mayor did not shut them down.

“Look, protest is part of the American tradition. I would argue those in the room that know their history, there’s a lot of protest that led to the United States of America,” de Blasio said at One Police Plaza after an NYPD promotions ceremony.

The protests were taxing for police officers — some were injured. But the city was never set ablaze.

Then on Saturday, Dec. 20, 2014, two police officers were shot in Brooklyn while sitting in their patrol car by a man who had driven up from Baltimore. Assailant Ismaaiyl Abdullah Brinsley had made comments on social media that indicated he wanted to kill NYPD officers as revenge for the deaths of Garner and Michael Brown.

The head of the union representing rank-and-file police stood outside the hospital where officers Rafael Ramos and Wenjian Liu had been pronounced dead and went after de Blasio.

“There is blood on many hands tonight,” railed Patrolmen’s Benevolent Association president Patrick Lynch. “That blood on the hands starts on the steps of City Hall in the office of the mayor.”

At the funerals days later, many police turned their backs on the mayor. The flagrant defiance had the unlikely effect of making de Blasio a sympathetic figure in a tragedy that stunned the city right before Christmastime.

A public cooling-off period followed.  During de Blasio’s state of the city speech, he made only a passing comment about police and community relations. The bulk of the speech was dedicated to his affordable housing agenda.

Then in May, another police officer, Brian Moore, was killed in an unrelated incident, adding to the department's sense of grief and frustration.

But at Moore's funeral, officers did not turn their back on de Blasio.

The department is changing. New police policies are starting to show promising results. There's a wholesale retraining underway at the NYPD and 1,300 new cops are being added to the force.

The mayor is clear that there will be no backing away from broken windows enforcement. But at the same time, his commissioner is directing the NYPD to walk the streets and forge ties with the community in an effort to prevent the next tragedy.

Speaking at a memorial for Garner this week, at the same church in Staten Island where his words had inflamed some on his police force last year, de Blasio offered a message calibrated by the lessons learned after Garner's death.

“It should not need to be said, but until we make more progress, I’ll say it again: black lives matter,” said de Blasio. But in a nod to the deaths suffered by the department, he added, “Also we should say, blue lives matter.”