How did Hitler come to power? He was elected.
Why was he elected? Popularist, racist rhetoric, and German hope/pride for a turn around in fortunes from their disastrous World War 1 (and complicated communist and nationalist militia conflicts through Europe in the 20's and 30's creating a penchant for violence in European governments)
What did he do when elected? Intimidated, used thugs, changed rules, and turned a democracy into a dictatorship.
How was this possible? Business, citizens, interest groups (and yes, the Christian Church) accepted erosions of democracy
To the extent any current politician tries to erode democracy, the comparison is apt.
Why do you say democracy can't turn up disasters capable of creating Nazi Germany or Putin's Russia, when that is exactly what happened.
Hitler didn't set up concentration camps until he had total power. He didn't get elected on a platform of executing Jews and dissidents. But these things happen after a democracy allows itself to become undemocratic.
I specifically said the comparison is troubling to some (who are likely to blow up like you did) if you think people are saying that a current person, compared to Hitler, is executing civilians. That is the sort of thing happening in authoritarian states still today, but thankfully not here. I'd like to keep it that way. Keeping a free press, independent judiciary, transparent government, are important pillars of free democracies (more so than a house of review, which is still another safe guard).
But the issue is how do authoritarian states get that way, if they were once democracies (as Nazi Germany was). A house of review is absolutely useless in stopping an elected leader unless they are interested in keeping democracy over their own power (consider some senators in the USA who just agreed that Trump is fine to rig elections in his favour, if he thinks he is the best person to be president).
You've entirely missed the point if you think we need only become wary of authoritarian action after execution camps are set up or opposition parties are banned. By then it is too late.