Pay no attention to that 1966 date. This film is merely a cobbled together, highly edited version of 1940's twelve-part serial Flash Gordon Conquers the Universe. There's Buster Crabbe as Flash, Charles Middleton as Ming the Merciless, Frank Shannon as Dr. Zarkov, and Carol Hughes as Dale Arden.
Ming, up to his old tricks, is spreading the Purple Death over Earth by way of deadly dust. Flash, Dale, and Zarkov head off to the planet Mongo to foil mean old Ming. Complications ensue.
Sometimes you need something completely mindless. I'd much rather watch this than this week's follies de Trump.