Emboldened by the mainstreaming of hard-right politics ahead of a presidential election cycle, white nationalist and anti-LGBTQ+ groups increased to record levels in the United States last year, according to the Southern Poverty Law Center’s latest annual report on hate and extremism released Tuesday.

The terms “alt-right,” “far-right,” and “radical right” get thrown around a lot these days. But there’s actually very little research on what those...