These days it’s a dumb online-only meme for anyone to the left of Bernie Sanders. It’s todays “commie.” It’s a thought-terminating chiché for the purposes of shutting out those to one’s left.

https://en.wikipedia.org/wiki/Tankie#Modern_Internet_uses but actually https://www.joewrote.com/p/jfk-files-reveal-the-cia-role-in

The Hungarian Freedom Fighters were [Central Intelligence] Agency sponsored.