A new FBI report on hate crimes tells a sobering story. For the second year in a row, police departments across the country reported a rise in the number of crimes motivated by bias.

In 2016, the FBI counted 6,121 reported incidents nationwide — an increase of 4.6 percent from 2015, during which 5,850 cases were reported. That number, in turn, marked a 6.8 percent increase in reported hate crimes over 2014. Roughly 58 percent of such attacks last year were motivated by racial bias, of which about half targeted African Americans. Of the 21 percent of crimes fueled by animosity toward the victim’s religion, more than half the attacks were aimed at Jews, a quarter at Muslims.

The sharp rise in crimes against Muslims and people of Arab descent is particularly troubling. Racially motivated attacks on Arabs jumped 38 percent from 2015, the first year in which the FBI requested data on such crimes. And attacks on Muslims, which spiked 67 percent in 2015, rose an additional 19 percent last year to more than 300 reported incidents. That makes 2016 the year with the highest number of hate crimes against Muslims since 2001, following the 9/11 attacks.

Meanwhile, crimes against Latinos and against white people rose 15 percent and 17 percent, respectively, from 2015. Crimes against transgender people went up 44 percent.

The FBI’s report doesn’t draw conclusions as to what might be behind this disturbing rise in hate. But it’s noteworthy that many of the groups against whom crimes rose by double digits were the focus of inflammatory rhetoric by Donald Trump over the course of his presidential campaign. Likewise, the FBI data shows a sharp rise in bias-motivated incidents in the months around the 2016 election — confirming reports by the Anti-Defamation League and others of a surge of attacks on Muslims and Jews in the wake of Mr. Trump’s election.

“Hate crimes are different from other crimes,” FBI Director James B. Comey said in a 2014 speech. “They strike at the heart of one’s identity.” For this reason, it’s important that the United States be able to tackle this growing problem with the best data it can gather. The FBI’s statistics on hate crimes, while the best we have, are also incomplete — partly because it’s up to state and local police departments to decide whether to provide the federal government with their data. What’s more, a study by the Bureau of Justice Statistics suggests that many hate-crime victims never report the offense.

Police departments should work to provide the federal government with more complete data. But taking this rise in hate seriously also requires that law enforcement officials cultivate trust with the communities they serve. Victims need to know they will be treated with respect if they come forward — especially in the current political environment, where many may be particularly fearful.

The Washington Post