Suspect in murder of 10 people allegedly wrote doc endorsing "once-fringe racist" conspiracy theory claiming immigration is part of a plot to take power away from White people. Suspect indicated he was radicalized online; no evidence he watched Fox's hosts. But Washington Post points out that Tucker Carlson, among others, has been "an avid promoter of the thesis," mentioning "variations" on it in more than 400 episodes, per New York Times analysis.