
If you are wondering specifically just who the “growing extreme left” that JD Vance and Stephen Miller plan to “identify, disrupt, dismantle and destroy” might be, I think this clears it up:
In the latest example of his dangerous extremism, J.D. Vance has enthusiastically promoted a book that uses genocidal language to stoke hatred toward both liberals and progressives.
Unhumans, by right-wing conspiracy theorists Jack Posobiec and Joshua Lisec, offers a sinister thesis: Progressive-minded Americans are not humans. Instead, they are “communists.” In turn, the authors define communists as bloodthirsty “unhumans” hellbent on the destruction of civilization.
Right-wingers, they write, must stop these unhumans with a policy of “exact reciprocity.” This means doing exactly to these so-called unhumans what the authors claim the unhumans are planning to do to them.
The 283-page screed reads like an effort to incite a civil war. It strains to create a sense of urgent terror in its readers. On nearly every page, it demonizes and dehumanizes “the left”– a vaguely defined group that apparently includes journalists (“the unhuman-occupied media”) and people who believe in things like diversity, equity, social justice and the rule of law.
The definition is so broad that it seems most Democrats would qualify as unhumans.
Here’s Vance’s blurb:

Miller’s the one who wrote the speech calling Democrats vermin so I have to assume this comports with his understanding.