Was the Weimar Republic doomed?

[The Mikado]

Doomed from the outset? No. However, it essentially died in 1930 in the Brüning Chancellorship and it took two and a half years for people to notice.

[The Mikado]

I don't think there was any coming back for the Republic after nearly 3 years of accepting that the Reichstag was meaningless theater and the governing would happen by handpicked Chancellors abusing Presidential decrees by a decrepit and senile figurehead. The credibility of democratic government had already pretty decisively collapsed in Germany by the time Hitler became Chancellor.