There is no available evidence from the provided sources to verify Stephen Miller's claim about tapes showing federal workers and others celebrating the assassination of Charlie Kirk or constituting a domestic terrorism movement.
STEPHEN MILLER: "Tape after tape after tape of federal workers, bureaucrats, staffers in the Pentagon. Educators. Professors. Healthcare workers. Nursery nurses celebrating the assassination of Charlie Kirk. These are radicalized people. There is a domestic terrorism movement in this country."

FactVerify
Source: factverify.com
Key Evidence
No sources were found that mention tapes involving federal workers or others celebrating the assassination of Charlie Kirk or describing a domestic terrorism movement as stated by Stephen Miller.
What the Evidence Shows
The statement attributes serious allegations to a group of federal workers, educators, healthcare workers, and nursery nurses, claiming they are radicalized and involved in a domestic terrorism movement, specifically citing celebrations of an assassination. However, the search results provided contain no sources or evidence to support or refute these claims. Without independent verification, official records, credible news reports, or documented proof of such tapes or events, this claim remains unsubstantiated.
The lack of any corroborating information means it cannot be confirmed as true or false based on the current data.