The brazen murder of NYPD officers Wenjian Liu and Rafael Ramos, shot to death last weekend by Ismaaiyl Brinsley in some horribly misguided attempt at retribution over the deaths of Eric Garner and Michael Brown, is a tragedy. But it was made worse by NYPD union officials and allies, who cynically appropriated Liu and Ramos' deaths to bludgeon their political opponents.

Pat Lynch, the president of the Patrolman's Benevolent Association (New York's largest police union), all but accused Mayor Bill de Blasio of actual complicity in the murders, saying "that blood on the hands starts at City Hall in the office of the mayor," language echoed by the Sergeants Benevolent Association.

New York cops are used to getting their way. But they don't seem to realize how times have changed. And there's a good chance their fire-eating rhetoric could backfire.

First, the political context. Lynch and the PBA have been embroiled in a political fight with de Blasio, who was elected in part on a platform of restraining the police. The mayor has sharply curtailed stop-and-frisk, and has made some hesitant moves toward stricter scrutiny of cops using excessive force after Eric Garner was choked to death by police and his killer was not indicted.

De Blasio's relatively mild criticism of the non-indictment sparked bug-eyed outrage from police unions and their allies. Last week (before the shooting of Liu and Ramos), Lynch declared that de Blasio should not attend the funerals of policemen killed in the line of duty. NYPD officers turned their back on the mayor as he walked through a Brooklyn hospital to address the public about the murders. Lynch unsubtly threatened that unless de Blasio backed off, police would slow-walk enforcement of the law.

That last part seems nuts, but former NYPD commissioner Howard Safir agrees that cops may indeed sacrifice public safety to achieve political goals:

We should all be concerned about the reaction our police officers will have. I have seen times when police bashing has resulted in officers doing the minimum necessary to complete their tours and go home safely to their families. [Time]

Nice low crime rate you've got there, sure would be a shame if anything happened to it.

Reading past the unhinged rhetoric and threats, Lynch's actual position seems to be that the police deserve to be automatically exonerated whenever they injure or kill someone, regardless of circumstances, and should always receive unquestioning, worshipful deference. And this is in fact largely what cops obtain in American society.

The police are the third-most respected institution in the country (behind the military and small business). Cops are almost never indicted for anything, let alone convicted. Darren Wilson got off for killing Michael Brown, just like the cops that killed Garner, and the cops that killed John Crawford, McKenzie Cochran, Andy Lopez, Kimani Grey, Reynaldo Cuevas, Sean Bell, Prince Jones, Amadou Diallo, and many, many others. When a cop is charged with something, it's remarkable enough that "rare" goes in the headline.

But by stoking near-mutiny against the civilian leadership in New York, Lynch could potentially force a high-stakes confrontation he might well lose, and that could kneecap the cops' longstanding benefit of the doubt.

The problem with Lynch's blistering rhetoric is that it isn't remotely consonant with reality. Being a cop is not even in the top ten most dangerous professions. There were 97 fatal injuries among American police in 2013, a decline of 20 percent since 2012 and the lowest number since the series has been collected, according to the Bureau of Labor Statistics. Looking at the overall number of cops, that gives a fatality rate of about 12 per 100,000. A fisherman is over six times more likely to die on the job – and a logger 7.5 times more likely.

Crime is far, far lower as well. It isn't 1992 anymore, when thousands of New York cops swarmed City Hall and blocked the Brooklyn Bridge for an hour, in a similar protest again then-Mayor Dinkins' insufficient deference to the NYPD. Homicide has fallen by half since those days, and violent crime in general is down by something like 70 percent.

The tectonic plates of politics are shifting as crime continues to fall, year on year. In the days of the 20th century crime epidemic, the police enjoyed a broad mandate to crack down on crime, and largely unquestioned respect (among whites at least) for doing a dangerous job. Both those things aren't nearly as secure as they once were. The reality that America in general, and New York in particular, is a much less dangerous place than 30 years ago, will percolate through the popular consciousness.

De Blasio would clearly rather not get in a real political fight with the NYPD, which still enjoys wide public support. But the unions' rank insubordination or outright mutiny might force his hand. The police demanding de facto immunity from prosecution is much more politically risky than it was in 1990. Not to mention that de Blasio won election with over 73 percent of the vote, on a platform of restraining police violence.

Lynch and Co. might try just respecting basic democratic legitimacy. It turns out that people have a First Amendment right to protest. And elected political leadership ought to have control over the exercise of state violence.