> Hitler is the classic example of someone who came to power
> constitutionally, and then proceeded to gut the constitution.
Completely changing the subject: People say that a lot, and it's annoyingly inaccurate. By the time Hitler had come to power the conservatives were well on their way to gutting the Weimar democratic system via emergency powers (e.g. http://en.wikipedia.org/wiki/Preu%C3% 9Fenschlag , although I can't vouch for the article's accuracy). And he came to power in large part because the conservatives thought they could use him as an anti-democratic force.
The history is worth remembering, among other reasons, because Russia is in many ways similar to Weimar Germany: an insecure former empire whose fall is blamed on others, and a democracy fatally undermined by leaving in place military and government bureaucracies that still looked back to the authoritarian past. Russia did have the looting and resulting oligarchs for a while, but the authoritarian state is now firmly back on top.