Why Did The FBI Undercount Antisemitic Hate Crimes?

In a typical year, the numbers are the story: Jews are about 2% of Americans but have topped the FBI's religiously motivated hate crime category "since 1991, often registering between 9-13% of overall hate [crime] totals." This year, though, the story is why the FBI's data so undercounted antisemitic hate crimes that Congress wants revised statistics.