Do please rent / buy Triumph of the Will.
It is probably the most brilliant piece of cinematic propaganda ever produced.
Also, before watching it, try to get your head in a receptive mode, not captive to the last 70 years' judgments.
Record what the film evokes in you, then think about what it evokes/tries to evoke versus what occurred when these folks acquired power.
Think about the folks who are not able to put themselves outside the moment, who get all swept up in the emotion generated by the film or similar products.
Then think of trying to make a rational argument against their man and their plan, when rational had nothing to do with their man & plan, to begin with.