On Saturday night, after Cole Tomas Allen’s alleged attempt to assassinate President Trump and administration officials at the White House Correspondents’ Dinner, a familiar ritual began on the internet: compiling a portrait of the shooter, based on the digital breadcrumbs of his online life. Over the past decade, this trail has frequently led to a similar place. The suspect in many cases turned out to be a white man radicalized by spending time in the internet’s dark crevices. Payton Gendron, who killed 10 people in 2022 at a grocery store in a predominantly Black neighborhood in Buffalo, New York, posted a manifesto that quickly circulated on 4chan, in which he included neo-Nazi imagery and described himself as an “ethno-nationalist.” Before Robert Bowers shot and killed 11 people in 2018 at a synagogue in Pittsburgh, he posted bigoted content on the far-right social-media platform Gab. Allen, a tutor who traveled from California to the Correspondents’ Dinner in Washington, D.C., with a shotgun, a handgun, and knives, according to authorities, does not fit that profile. The 31-year-old …