The Biden administration’s assessment that domestic violent extremism is one of the greatest threats facing the United States isn’t the first time the federal government has made such a declaration. Some 50 years ago, President Richard Nixon made a similar statement, deeming “revolutionary terrorism” as the gravest threat facing the homeland. Counterterrorism historians discussed the similarities between the two periods at an event held by the Cato Institute in Washington on Nov. 10, warning that some of the past incursions on civil liberties could be repeated today. Both eras are marked by the national security state turning its attention inward after an extended campaign overseas, said Faiza Patel, a codirector at the Brennan Center for Justice. “There was this shift [in the 1960s and 70s] from the idea of a communist threat that was instigated from overseas, to the leftist threat as envisioned as purely domestic. And as I think …