Mr. McCarthy did indeed lead the city’s data-driven CompStat system in the ’90s, which not only overlapped with Mr. Giuliani’s tenure, but also coincided with a sharp decline in the crime rate across nearly all major cities in the country, many without New York-style data systems or crackdowns on so-called quality-of-life crimes.

As the statistical adage goes, correlation does not imply causation. The verdict from mainstream sociologists and criminologists alike is that there is a clear and obvious reason for neither the widespread decades-long decline in violent crime nor its recent spike in big cities like Chicago.

When Mr. McCarthy came to Chicago in 2011, the city’s homicide rates had steadily declined to their lowest levels since the 1960s. After a troubling rise in 2012, the Chicago Police Department under Mr. McCarthy was under pressure to get the numbers down, and to his credit, it did.

Still, the specific forces behind the spikes and dips have vexed both independent observers and public servants honest about how unwieldy and multilayered the roots of violence are. A popular but unproven answer is the “Ferguson effect” (or in Chicago, the “Laquan McDonald effect”), which maintains that police officers are being undermined and unfairly maligned by politicians and the public and in response are retreating from proactive policing.

The “let cops be cops” solution — most recently peddled on “Fox & Friends” in light of the bloody weekend — feeds the delusion that police officers themselves can actually control crime, that the causes of and prescriptions for plagues like gun violence are untied to socioeconomic factors.

Giving the police more of anything — more numbers, more money, more liberties — to quell violence is still a reactionary, and thus limited, posture. And yes, so is simply calling for tougher gun laws (regulations the city of Chicago has, but its immediate surrounding area does not). To the communities affected, policing and gun laws are only parts of the puzzle.

Missing from Mr. Giuliani’s playacting concern for Chicago — and too often absent from the familiar pattern of reactions in our media — is an exploration of what the communities whose residents are being disproportionately shot and killed say they want.