National Violence & Harassment 19 Years After 9/11, Americans Still Fear Foreign Extremists, Yet Underplay Dangers of Domestic Terrorism Jeff Gruenewald, Joshua D. Freilich, Steven Chermak, William Parkin and Brent Klein Homegrown far-right extremism also poses a persistent and lethal threat to the lives and well-being of Americans. This risk is often underestimated because of the devastating impact of the 9/11 terrorist attacks.