Shootings and killings do not define Chicago. Nor does the threat of gun violence. Life in this busy, complex city feels safe enough to put a limit on fear. Crime is real, yet for most people, most of the time, it is also abstract.

The reality is different for Chicago police officers. With every shift they take, officers accept the risk that Chicago’s dark culture of gun violence will place them in danger. Or stop their lives cold. That has happened in three incidents in 2018, resulting in the deaths of four sworn members of the Chicago Police Department.

Last week, Officers Eduardo Marmolejo, 36, and Conrad Gary, 31, responded to a call for service on the Far South Side after a report of shots fired. They were on railroad tracks doing surveillance when they were struck and killed by a train. The deaths of these officers, young men who were in the early stages of their careers, is crushing for their families, their department, their city.

Grief and frustration feel heightened by the fact that two other CPD members were killed this year. In February, Cmdr. Paul Bauer, 53, was shot and killed while chasing a suspect to a stairwell outside the Thompson Center in the Loop. In November, Officer Samuel Jimenez, 28, was killed in the mass shooting at Mercy Hospital & Medical Center on the Near South Side. Dr. Tamara O’Neal, 38, and pharmacist Dayna Less, 24, also were slain in that incident.

Four officers down, four line-of duty deaths, in 10 months. Two police funerals completed, two more to be planned. The senselessness and relentlessness of gun violence in Chicago are measured by hundreds of homicides and thousands of shootings each year. From time to time that gun culture also is measured by the sacrifices made by police officers as they work to make the city safer.

Through Chicago’s history, hundreds of officers have died in the line of duty, many of them struck by bullets.

The circumstances of each officer’s death are unique, but as with the overall toll of gun violence, a sense of futility pervades: There’s no stopping the accessibility and ubiquity of illegal firearms here. Violent crime totals fluctuate; the readiness of some criminals to address their problems by pulling triggers endures.

Chicago has within it an intractable culture of shooting and killing, largely stemming from street gangs and the drug trade. Eradicating this scourge will take years or maybe generations of effort. That effort has to be as relentless as the bloodshed it seeks to curtail. Surrendering to the sense of futility that each killing brings isn’t an option.

We know that officers are doing all they can, each day and each shift, to protect the public, at the risk of their lives. Last week, two more members of the force, Officers Marmolejo and Gary, made that sacrifice. Chicago is in their debt.