I have just finished reading an excellent graphic novel biography of Hannah Arendt, and on p. 165 (below) is the core of her thinking, reflecting on how hell (as exemplified by the Nazi genocide of Jews) happens. Contempt for facts leads to concentration camps. I never realised though she thought both Nazi Germany and Stalin’s Russia were totalitarian – although my own modern take on it is similar (woke left and alt-right = the same underlying thing).
But yeah, check out p. 165 below (‘Benjamin’ is philosopher Walter Benjamin):

My key takeaway is that untruth is a good intentional tactic for political leaders who want totalitarian power. She also says:
The ideal subject of totalitarian rule is not the convinced Nazi or the convinced Communist, but people for whom the distinction between fact and fiction (that is, the reality of experience) and the distinction between true and false (that is, the standards of thought) no longer exist. (Arendt, 1968: 474)
So the current post-truth world is perfect environment for totalitarianism both from the left and the right. It works both through external and internal coercion:
Totalitarianism is never content to rule by external means, namely, through the state and a machinery of violence; thanks to its peculiar ideology and the role assigned to it in this apparatus of coercion, totalitarianism has discovered a means of dominating and terrorizing human beings from within.
Another similarity between now and Nazi Germany (through an Arendt lens) is the removal of distinction between private and public, and the elevation of subjective experience. Arendt thought emotions should stay in the private sphere as they are intensely subjective, and thus would impose their singular perspective on politics. The result of this in the case of Nazi Germany according to her was an insensitivity to reality (and thus the atrocities of genocide).
The graphic novel (which I got out of the library BTW) is The Three Escapes of Hannah Arendt: A Tyranny of Truth.
Truth and Politics
I only realised after reading Arendt’s later article Truth and Politics that actually ‘not telling the truth’ is an ‘expected’ / acceptable part of politics (it used to be called rhetoric – the art of persuasion). In the article, she also explores different types of truths (e.g., factual truth and philosophical truth) and explains why citizens must stand up for a factual account of reality (difficult in these ideological days!!).
A good overview (under 8 mins) of Truth and Politics in below video.