There's another reason for caution: Police agencies have long been unusually politically powerful. Politicians never want to purposely alienate anyone, but they are particularly wary of crossing the cops.
It's clear why.
People (read: voters) largely trust the police.
First and foremost, the police are popular.
Each year, Gallup polls Americans to evaluate how much confidence they have in various institutions. In the most recent iteration of that research, police were rated third-highest, behind the military and small businesses. Americans have more confidence in the police than they do in organized religion.
Compare that with confidence ratings for Congress, which have fallen, continue to fall, and don't have much further they can drop. Branches of the military, the institution in which Americans have the most confidence, can't (and shouldn't, for clear reasons) endorse elected officials. But local police forces and, more specifically, local police unions, can and do.
People who trust the police more also vote more.
Not only that, but the police have stronger support from groups that vote more frequently. Below, data from Gallup breaking down how honest the police are perceived to be by political party and age.
Gallup also found that nonwhite Americans were substantially less likely to share white Americans' confidence in the police. Forty-eight percent of nonwhites had a "great deal" or "quite a lot" of confidence in cops, compared to 68 percent of whites.
Whites, Republicans, and older Americans are also more likely to regularly vote, including in off-cycle elections where local politicians are on the ballot.
Politicians love to say they're endorsed by police -- and fear a "soft on crime" image.
If you've ever been near a television during October in an even-numbered year, you've seen a police officer on television, describing why Candidate X is backed by the police. If you've ever actually looked at the mail you receive that same month, you'll see pieces of mail that, somewhere, have a little gold badge prominently displayed.
Getting the endorsement of the police is not a golden ticket to election. But it beats the alternative: Police suggesting that a candidate will be dangerous for the community. Think of the Willie Horton ad President George H. W. Bush ran against Michael Dukakis in the 1988 presidential race, a revolving door in a prison gate. Ads like these, featuring local cops in recognizable communities, are the nightmares that keep politicians up at night.
Politicians and police have to work together after Election Day.
Once he did, de Blasio quickly extended an olive branch,appointing veteran cop Bill Bratton to lead the NYPD. The move was praised by police and was greeted warily by the progressive base that swept de Blasio into power. But, it was a reflection of political reality: The police had just become de Blasio's employees, and he needed their help.
Earlier this month, that relationship became clear. De Blasio defended Bratton following harsh criticism of the NYPD following the death of Eric Garner, the man who died after a police officer put him in a chokehold on Staten Island. Candidate de Blasio was in the unusual position of being able to criticize the NYPD's behavior, given his massive lead in the polls.
But Mayor de Blasio is responsible for the NYPD, so the agency gets a level of deference that it might not otherwise have received. He hired the guy that runs the police; what they do is a reflection of him. Cautiousness to that end can be tricky.
On MSNBC, Ferguson Mayor James Knowles defending police conduct: “I can’t second guess these officers”
— Michael Calderone (@mlcalderone) August 14, 2014
In many places, there's an additional concern for elected officials: Negotiations over salary and benefits. Police officers are not allowed to strike and, in many places, have a binding arbitration process that is the final step in any dispute over pay and benefits. For elected officials with fiduciary responsibility over budgets, keeping a close relationship with police makes sense.
Add all of this up, and the political potency of the police is obvious. Voters love them, and politicians want their help before and after election day. So when a police force takes a step past its boundaries, as it appears to have done in Ferguson, politicians are rarely eager to be the first ones to point it out.