ANY DISCUSSION of the complex subject of law enforcement in the United States should start with an acknowledgment that police work is dangerous. Several dozen officers are killed in criminal acts each year, and dozens more die in accidents — to say nothing of hundreds who are wounded. The ambush shooting in Los Angeles on Saturday of two sheriff’s deputies, who were seriously injured in the attack as they sat in their patrol car, was a monstrous act of lawlessness. It was also a reminder of what is too often ignored: that many police are justified in feeling threatened as they patrol the communities they are charged to serve and protect.

It is chilling to watch a video of the incident, in which a man walks up the street and, on reaching the patrol car, suddenly draws a handgun and fires repeatedly through the passenger-side window. Both officers, sheriff’s deputies for just 14 months, were struck, one of them a 31-year-old mother, the other a 24-year-old man. The gunman is now the subject of a massive police manhunt.

Major political figures condemned the shooting. Some seized on video footage of a handful of individuals who yelled anti-police slogans at the entrance of the hospital where the officers were brought for treatment; one or two men could be heard saying “We hope they die.” The suggestion, from some on the right, is that the summer’s protests against police violence, or advocacy for police reform or racial justice generally, amount to a broader incitement to violence against the police.

In fact, most of the demonstrations that followed George Floyd’s killing in May at the hands of police in Minneapolis, while often angry, did not feature calls for retribution. And it’s preposterous to equate support for public safety reforms with a license for violence against law enforcement.

The Internet, on the other hand, is a different story. A report released Monday by the Network Contagion Research Institute identified the spreading online use of toxic, anti-police memes and slogans, some of which also crop up in graffiti scrawled on buildings and statues, from left-wing individuals and groups. One such slogan is “ACAB,” which stands for “All Cops Are Bastards.” At least as concerning are images on social media showing police being shot or their vehicles burned.

The report’s authors pointed out that right-wing extremists, including white supremacists, have been responsible for much more violence nationally, as federal officials have also emphasized. That doesn’t mean that online provocateurs who endorse violence against the police should be shrugged off.

America is in a moment of rage. Hours before the shooting Saturday in Los Angeles, more than 200 people there protested the death of a Black man, Dijon Kizzee, who was shot to death on Aug. 31 by LA sheriff’s deputies. The sheriff’s office said he was riding his bicycle, fled on foot when the deputies tried to apprehend him for an unspecified violation, then punched a deputy who chased him. The deputies opened fire when they thought they saw him reaching for a gun, the sheriff’s office said. Activists and Mr. Kizzee’s relatives say he was unarmed when deputies shot him in the back.

Systemic reforms are one thing. Wise leaders who exert a calming influence are another. Both are badly needed at the moment.

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