First off, this dead horse has been beaten until it's just a greasy smear on the asphalt.
Secondly, there are similarities and there are differences. Could the same thing happen again the same way? Likely not. Could things go to hell in a handbasket in ways that are somewhat similar, and yet different enough to account for the passage of time, economic and geopolitical differences, etc? Maybe, but there are certain pre-requisites that need to be satisfied first, and it's not clear that that's the case yet, or ever.
The use of demagoguery in politics has not started with Hitler and will not end with Trump. Ancient Greeks and Romans did it occasionally. McCarthy and Huey Long did it too. The examples go on and on, and every such figure has different skills and characters and attributes. One thing to keep in mind is that Hitler was really, really freaking good at it; he's set a very high bar, if that's the right word for it. He makes the others in this category look like amateurs in comparison.
Also, the socio-economic conditions in Germany in early 20th century were pretty spectacularly bad. I'm not saying that everything is just sunshine-and-bunnies now in the world, but there's nothing going on like the triple whammy of global great depression, hyperinflation, and national humiliation after losing a great war, that helped the ascension of Nazism to political hegemony.
Time will tell, as always.
P.S.: For a history of the rise and fall of Nazism in Germany, along with plenty of details about social, political and economic conditions that accompanied those events, see the Third Reich trilogy by Richard Evans. Link to the first volume:
Anyway, the Nazis still have followers today. I have been doing research on a younger generation (that is, people with birth years like my parents, in the 1930s) of neo-Nazis in the postwar era, and there are even people younger than that (birth years in the 1980s and 1990s) who haven't learned enough about Nazi history to know that the Nazis are no example worth following for anyone. We must never forget.
I get good book recommendations here on HN all the time, most recently a set of books about German history, but we hardly ever have extended book discussions here.
a) The fact that by 1933, the majority of the population was voting for parties that were explicitly against the democratic system. Even if there was no majority for the Nazis, there was also no majority in defense of protection of constitutional limits on power.
b) The government bureaucracy and much of the elite (including the then President, Hindenburg, and old military man) were loyal to the State/Realm (Reich) to which they swore their oaths, but not to the democratic order and the constitution, and so were not functional impediments to Nazi power. I was also struck, when reading about their actions and motivations, how little they realized that democratic protections and limits on power protected them as well - when the Nazis took power, the conservative establishment was removed from civilian power by force or the threat of force, using powers that the conservatives had originally intended for use against the Left.
c) Once the Nazis came to power, they succeeded in instilling in the German public apathy and an unwillingness to get involved in political opposition (though not necessarily active devotion to Nazi ideology). A fanatical minority can do a lot of damage if the majority is apathetic or is distracted by more popular policies (like national greatness and revenge on the WWI Allies).
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