Exactly like the classic fallacy they love to use:

Lib cites public CIA talking point as proof we need to bomb X country. You say, "The CIA lies about this stuff all the time, here's an internal CIA memo where they discuss lying and controlling the media to generate fervor and consent for killing these other people" The lib says, "Aha, so the CIA isn't a trustworthy source but you're citing them here"

This way they can A. Dismiss criticism against CIA B. Maintain that the CIA is a trustworthy source. C. Prevent you from citing the CIA despite them supposedly believing it is trustworthy (when it says stuff they like).

Unlike modern libs, Hitler had to engage in the material reality of Russia on some level because he was fighting a war against it, rather than just going off of vibes and half-remembered Red Scare propaganda