Shocking acts of terrorism have erupted from violent American far-right extremists in recent years, including the 2015 mass murder at a historic Black church in Charleston and the January 6, 2021, attack on the U.S. Capitol. These incidents, however, are neither novel nor unprecedented. They are the latest flashpoints in a process that has been unfolding for decades, in which vast conspiracy theories and radical ideologies such as white supremacism,...