The go-to tactic for downplaying political terrorism and mass shootings is to blame the attackers’ violence on “mental illness.” A person who would crack an 82-year-old man’s skull with a hammer, or shoot up a supermarket, synagogue, or school, is no doubt mentally unwell. But what triggers troubled people to lash out violently? What determines their choice of targets? Those questions become more urgent when you consider that David DePape, the man accused of trying to kill Nancy Pelosi’s husband, shares a belief system with literally tens of millions of Americans: The 2020 election was stolen, Covid vaccination was tyranny, a Jewish cabal controls the world, legions of pedophiles are grooming children, and white men are now our society’s most persecuted victims. “He really believed in the whole MAGA, ‘Pizzagate,’…