As the homicide rate climbed through a year of pandemic-imposed shutdowns and civil unrest, officials held firm to their belief that the rise was driven by that exceptional set of circumstances. As life returned to normal, the theory went, the killings would slow. But even as coronavirus restrictions have been lifted and protests have quieted in recent months, the violence has not subsided. Indeed, it has continued to grow. And now, local leaders are grappling with a possibility they had long feared: that a decades-long era of declining murder rates in America’s cities may be over, and that the increased killings may be here to stay. “There’s nothing,” said Jackson, “that’s going to bring this down in the near future.” Officials and criminal justice experts offer abundant reasons: A nation awash in guns, now more than ever. Deep mistrust between police departments and the communities they serve, particularly in high-poverty areas. The still-painful stresses caused or exacerbated by the pandemic. A cycle of violence that, once set in motion, is hard to break. “The thing about violence is that it builds on itself. It cascades,” Princeton sociologist Patrick Sharkey said. “Each shooting brings the possibility of a reprisal.”