In March, an unnerving statistic began appearing in the headlines of mainstream news reporting: Donald Trump’s 2016 campaign rallies had produced a staggering 226% increase in hate crimes. For many liberals, a surge in hate-fueled violence probably seems self-evidently connected to Trump’s cruel remarks about specific minority groups, Mexicans, Muslims, etc. When the FBI reported late last year that hate crimes had increased 17% from 2016 to 2017, it seemed to confirm a certain narrative: Look around, and you will see that America has become a more spiteful place. But there’s a big problem with this thinking: The numbers don’t add up. Counting them is difficult work, and many of the organizations tasked with doing so routinely inflate them. Worse, media outlets that report on the hate trackers’ findings are careless in their descriptions of...