...And that's why it was so scary.
This is a thriller. The premise is Hitler has some how come through time and believes fate has brought him here to clean house (again). However, the film was actually using this metaphor to describe the coming of the next Führer if we're not careful. If we let down our guard we absolutely WILL see the rise of the next Adolf Hitler.
The character of Hitler spoke the truth, mostly. His rhetoric cut to the heart of today's problems. It was a German production so, obviously, he spoke directly to German issues but again, Germany was just the stage and Hitler the puppet. The puppeteers were revealing a global truth wrapped in a local narrative.
Recall the time Angela Merkel, today's German Chancellor, called G.W. Bush on 9/11 and the subsequent "War on Terror" saying something to the effect of, "We've seen this before...!" THIS is what the movie is getting at.
This film is filled with amazing though often chilling street interviews featuring Hitler interrogating work-a-day people. Many of the younger of these people so open to the apparent humor or irony were embracing him, taking "Hitler selfies" - other older spectators and interviewees apparently LONGED for someone to take the reins and whip (Germany) into shape, getting rid of "suspicious-looking, bearded Salafists", etc. And these were not actors. The film was illustrating for you how Hitler rose to power the first time and how easily and quickly it could happen again.
This was a beautifully done movie. I have the book as well and I prefer the movie.