Americans who volunteered to fight fascists prior to WWII were deemed, as Umberto Eco notes, “‘premature anti-fascists’—meaning that fighting against Hitler in the 40s was a moral duty for every good American, but fighting against Franco too early, in the 30s, smelled sour...

https://twitter.com/ExExtremist2/status/1805735038136295570

...because it was mainly done by Communists & other leftists.”

This term was oft use to denote someone as “communist” by the FBI & Red Scare McCarthyists.
A Spanish Civil War antifascist, Bernard Knox wrote of 1st being called the term in amesmerizing 2001 LA Times essay...

CONFIRMED: NAZIS COWERED BUTTE-SILVER BOW COUNTY INTO BANNING LIBRARY HISTORY LECTURE
Adria Jawort (me) was banned from doing history lecture as Nazi's brag of "campaign of complaints."
Officials also cite drag ban law as applicable to trans ppl.
#MTnews #MTpol At 11:14 am June 1 I received an email from an apologetic library employee who informed me Chief Executive JP Gallagher and County Attorney Eileen Joyce "have decided that it is too much of a legal risk to have a transgendered person in the library. I really regret this.” (sic)