A Face in the Crowd is a good one from Elia Kazan. Though not 100% about politics, it is about the cult of personality and how it bleeds over into everything including politics.
Also known as "the Glenn Beck story."
The Next Man I've seen and enjoyed. Directed by Franklin J. Schafner, who also went on to fame directing
Planet Of The Apes (1968),
Patton(1970),
Nicholas and Alexandra (1971), all of which won and/or were nominated for multiple Academy Awards. And
The Boys From Brazil (1977).