The Sixties and early seventies were a great time for conspiracy theories from the Kennedy Assassination to Watergate. A short after the later Alan J Pakula produced what is now known as the Paranoia Trilogy consisting of the films Klute, The Parallax View and All the Presidents Men. Then conspiracies were all on the left with the CIA and the deep state deemed responsible for all ills.
Today it’s the right who are convinced that shadowy global forces are gathering to destroy America. For this reason, the trilogy is fascinating to watch now, and of course, all the films hold up to pretty well. It’s definitely worth a couple of evenings to watch them back to back and remind yourself that conspiracy theories are not new and they’re not going away anytime soon
Popgun 
You can add ‘The Conversation’ into the paranoid mix as well…and even ‘Three Days fo the Condor’ probably gets a nod.
Absolutely. I think both work well as explorations of paranoia